<?php
error_reporting(-1);

function getBalanceInFuture($credit,$percent,$comission,$payment,$payout,$month) {
	for ($i=1;$i<=$month;$i++) {
    if ($payment==7777) {
    $credit = $credit + $credit * $percent + $comission + $payment - $payout;
    $payment++;}
    else { 
    $credit = $credit + $credit * $percent + $comission - $payout;
    }
	}
	return $credit;
}
$homoTotal= getBalanceInFuture(39999,0.04,500,0,5000,11);
$softTotal= getBalanceInFuture(39999,0.03,1000,0,5000,11);
$strawberryTotal= getBalanceInFuture(39999,0.02,0,7777,5000,11);
echo "За 11 месяцев школьник будет должен банку {$homoTotal}руб.\n";
echo "За 11 месяцев школьник будет должен банку {$softTotal}руб.\n";
echo "За 11 месяцев школьник будет должен банку {$strawberryTotal}руб.\n";