<?php

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

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

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

    return $paymentTotal;
}

$creditBalance = 39999;
$monthlyPayment = 5000;

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

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