<?php

error_reporting(-1);

$creditBalance  = 40000;
$percent        = 1.03;
$servicePayment = 1000;
$monthlyPayment = 5000;
$paymentTotal   = 0;

for ($month = 1; $month <= 20; $month++) {
    $creditBalance = ($creditBalance * $percent) + $servicePayment - $monthlyPayment;
    $paymentTotal  = $paymentTotal + $monthlyPayment;
    echo "{$month} месяц спустя: долг = {$creditBalance} руб, выплачено всего {$paymentTotal} руб. \n";
    
    if ($creditBalance < 5000) {
        $monthlyPayment = ($creditBalance * $percent) + $servicePayment;
        $paymentTotal   = $paymentTotal + $monthlyPayment;
        echo "С меня хватит! Выплачено всего {$paymentTotal} руб. \n";
        break;
    }
}

?>