<?php

error_reporting(-1);
header("Content-Type: text/plain; charset=utf-8");

$monthlyPayment = 5000;
$creditSum = 39999;

function getTotalAmountOfPayments($creditBalance, $paymentTotal, $percent, $servicePayment, $monthlyPayment) {
    do {
        $creditBalance = ( $creditBalance * $percent ) + $servicePayment;

        if ($creditBalance <= $monthlyPayment) {
            $monthlyPayment = $creditBalance;
        }
        $creditBalance -= $monthlyPayment;
        $paymentTotal += $monthlyPayment;
    } while ($creditBalance > 0);

    return $paymentTotal;
}

$homoCreditTotal = getTotalAmountOfPayments($creditSum, 0, 1.04, 500, $monthlyPayment);
$softBankTotal = getTotalAmountOfPayments($creditSum, 0, 1.03, 1000, $monthlyPayment);
$strawberryBankCreditTotal = getTotalAmountOfPayments($creditSum, 7777, 1.02, 0, $monthlyPayment);

echo "Сумма выплат в первом банке - {$homoCreditTotal} \n";
echo "Сумма выплат во втором банке - {$softBankTotal} \n";
echo "Сумма выплат в третьем банке - {$strawberryBankCreditTotal} \n";