<?php
 
error_reporting(-1);
 
function getSum ($percent, $tax, $account, $creditSum, $payout) {
	$paymentTotal = 0;
	$creditSum = $creditSum + $account;
	for ($i ; $i < 100 ;$i++) {
		$creditBalance = $creditSum * $percent - $payout + $tax;
		//надо подумать над другим ограничением цикла
		$paymentTotal +=  $payout;
		$creditSum = $creditBalance;
		if ($creditBalance < 0) {
			$paymentTotal += $creditBalance;
			break;
		}
	}
	return $paymentTotal;
}
$creditSum = 39999;
$payout = 5000;
 
$homoCreditBank = getSum (1.04, 500, 0, $creditSum, $payout);
$softBank = getSum (1.03, 1000, 0, $creditSum, $payout);
$StrawberryBankTotal = getSum (1.02, 0, 7777, $creditSum, $payout);
 
echo "homoCreditBank {$homoCreditBank} руб \n";
echo "SoftBank {$softBank} руб \n";
echo "StrawberryBankTotal {$StrawberryBankTotal} руб \n";

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