R function for finding mean of a population greater than a specific value

I’m currently learn R and I’ve hit a rock. How do I present the code for the proportion of the population taller than 15m. (Question 5 in the picture)number 5 question for a randomly generated sample in a dataset

Tried using a for loop but can figure out what to input for the vector. I’m expecting a cut of of values from 15m and above