<?php
$n = 6;
//инициализация
$start = microtime(true);


	$arr = [
	0=> "A",
	1=> "Б",
	2=> "В",
	3=> "Г",
	4=> "Д",
	5=> "Е",
	6=> "Ж",
	7=> "З",
	8=> "И",
	9=> "К",

	];

	function getChisloAndStr ($n)
	{
		$arr = [
	0=> "A",
	1=> "Б",
	2=> "В",
	3=> "Г",
	4=> "Д",
	5=> "Е",
	6=> "Ж",
	7=> "З",
	8=> "И",
	9=> "К",

	];
		$stroka = "";
		$chisla= "";

		for ($i = 1; $i<= $n; $i++)
		{
			$temp  = rand(0,9);
			$chisla .= $temp;
			$stroka  .= $arr[$temp];
		}
		$chisla = intval ($chisla);
		$res [0] = $chisla;
		$res [1] = $stroka;
		return $res;
	}

	$res1 = getChisloAndStr($n);
	$res2 = getChisloAndStr($n);
	$answerChislo = $res1[0]+$res2[0];


	$int = preg_split('//',$answerChislo);
    array_pop($int); array_shift($int);

    $answerSTR = $res1[1]."+".$res2[1]."=";
    for ($i=0; $i<= mb_strlen($answerChislo)-1;$i++)
	{
		$answerSTR .=  ($arr[$int[$i]]);

	}
	printf($answerSTR."<br>");
    printf($res1[0]."+".$res2[0]."=".$answerChislo."<br>");
$end = microtime(true);
$time = $end - $start;
printf('Время работы скрипта: %.7F сек.', $time);