Random string from this json php

<?php
$data = file_get_contents('https://ipinfo.io/AS7018/json?token=b7570cede7fcc9');
$x=json_decode($data);
$result = $x->{'prefixes'}[0]->{'netblock'};
echo $result;
?>

how do i use the random string netblock from this json. is there anyone who can provide code samples. Thank