How to start the functions from another file on this code [duplicate]

Recently I have been working on a videogame with Pygame, and I have already created the menu on one file, the game functions (sums) on another one, and the entry box (where the user writes the answer) on another one. I would like to start the game function (the sums) when I press the "Start" button of the menu. The names of each file are those: Menu - Suma - InputBox

Here is the code of the menu.

import pygame
import pygame_menu

pygame.init()
#Size and name of the window
surface = pygame.display.set_mode((600, 400))
pygame.display.set_caption("Projecte MatZanfe")

font = pygame_menu.font.FONT_8BIT
font1 = pygame_menu.font.FONT_NEVIS

menu = pygame_menu.Menu('Projecte MatZanfe', 600, 400,
                       theme=pygame_menu.themes.THEME_SOLARIZED)

user_input = menu.add.text_input('User: ', font_name = font1, font_color = 'blue')

age_input = menu.add.text_input('Age: ', font_name = font1,font_color = 'Black')
menu.add.button('Start', font_name = font, font_color = 'green')
menu.add.button('Exit', pygame_menu.events.EXIT, font_name = font,font_color = 'red')
menu.mainloop(surface)

Here is the code that contains the game itself (the sums).

import pygame
import random
from InputBox import InputBox
from pygame import mixer
pygame.init()

clock = pygame.time.Clock()
surface = pygame.display.set_mode((600, 400))
pygame.display.set_caption("Projecte MatZanfe")
font = pygame.font.SysFont('comicsans', 50)
base_font = pygame.font.Font(None, 32)
user_text = ''
color_active = pygame.Color('lightskyblue3')
running = True
points = 0

def start_the_game():
    x = random.randint(0, 10)
    y = random.randint(0, 10)
    is_correct = False
    return x, y

def display_the_game(x, y):
    # Variables
    z = x + y
    surface.fill((255, 70, 90))
    text = font.render(str(x) + "+" + str(y), True, (255, 255, 255))

    text_surface = base_font.render(user_text, True, (255, 255, 255))
    surface.blit(text, (260, 120))
    input_box.draw(surface)
    punts = font.render("Puntuació: " +  str(points),True, (255,255,255))
    surface.blit(punts, (350,30))
    titolsuma = font.render("SUMA (1)", True, (0,0,0))
    surface.blit(titolsuma,(10,20))

x, y = start_the_game()
input_box = InputBox(190, 250, 200, 32)

while running:
    clock.tick(60)
    for event in pygame.event.get():
        if event.type == pygame.QUIT:
            running = False
        else:
            result = input_box.handle_event(event)
            if result != None:
                if int(result) == int(x) + int(y):
                    points = points + 5
                    mixer.music.load('StarPost.wav')
                    mixer.music.play(1)

                # create new random numbers
                x, y = start_the_game()

                # reset input box (just create a new box)
                input_box = InputBox(190, 250, 200, 32)


    display_the_game(x, y)
    pygame.display.update()

pygame.quit()

And finally here is the code from the imported InputBox (don't know if I actually need to use it).

import pygame


pygame.init()
surface = pygame.display.set_mode((600, 400))
COLOR_INACTIVE = pygame.Color('lightskyblue3')
COLOR_ACTIVE = pygame.Color('black')
FONT = pygame.font.SysFont('comicsans', 32)
base_font = pygame.font.Font(None, 32)
color_active = pygame.Color('lightskyblue3')
user_text = ''


class InputBox:

    def __init__(self, x, y, w, h, text=''):
        self.rect = pygame.Rect(x, y, w, h)
        self.color = COLOR_INACTIVE
        self.text = text
        self.txt_surface = FONT.render(text, True, self.color)
        self.active = False

    def handle_event(self, event):
        if event.type == pygame.MOUSEBUTTONDOWN:
            # If the user clicked on the input_box rect.
            if self.rect.collidepoint(event.pos):
                # Toggle the active variable.
                self.active = not self.active
            else:
                self.active = False
            # Change the current color of the input box.
            self.color = COLOR_ACTIVE if self.active else COLOR_INACTIVE
        if event.type == pygame.KEYDOWN:
            if self.active:
                if event.key == pygame.K_RETURN:
                    user_input = self.text
                    self.text = ''
                    self.txt_surface = FONT.render(self.text, True, self.color)
                    return user_input
                elif event.key == pygame.K_BACKSPACE:
                    self.text = self.text[:-1]
                else:
                    self.text += event.unicode
                # Re-render the text.
                self.txt_surface = FONT.render(self.text, True, self.color)

    def update(self):
        # Resize the box if the text is too long.
        width = max(200, self.txt_surface.get_width()+10)
        self.rect.w = width

    def draw(self, screen):
        # Blit the text.
        screen.blit(self.txt_surface, (self.rect.x+5, self.rect.y+5))
        # Blit the rect.
        pygame.draw.rect(screen, self.color, self.rect, 2)



def main():
    clock = pygame.time.Clock()
    input_box2 = InputBox(190, 250, 200, 32)
    input_boxes = [input_box2]
    done = False

    while not done:
        for event in pygame.event.get():
            if event.type == pygame.QUIT:
                done = True
            for box in input_boxes:
                box.handle_event(event)

        for box in input_boxes:
            box.update()

        surface.fill((255, 70, 90))
        for box in input_boxes:
            box.draw(surface)

        pygame.display.flip()
        clock.tick(30)


if __name__ == '__main__':
    main()
    pygame.quit()