<?php
error_reporting(-1);

function getBalanceInFuture($credit, $percent, $comission, $payment, $payout, $total)
{
    
    $total  = $total + $credit * $percent + $comission + $payment;
    $credit = $credit + $credit * $percent + $comission + $payment - $payout;
    
    for (; $credit >= 0; $credit -= $payout) {
        $total  = $total + $credit * $percent + $comission;
        $credit = $credit + $credit * $percent + $comission;
        
    }
    
    return $total;
}
$homoTotal       = getBalanceInFuture(39999, 0.04, 500, 0, 5000, 39999);
$softTotal       = getBalanceInFuture(39999, 0.03, 1000, 0, 5000, 39999);
$strawberryTotal = getBalanceInFuture(39999, 0.02, 0, 7777, 5000, 39999);
echo "Школьник будет должен банку {$homoTotal}руб.\n";
echo "Школьник будет должен банку {$softTotal}руб.\n";
echo "Школьник будет должен банку {$strawberryTotal}руб.\n";