<?php

// 3
function add($a, $b) {
    return $a + $b;
}
function sub($a, $b) {
    return $a - $b;
}
function mul($a, $b) {
    return $a * $b;
}
function rem($a, $b) {
    return $a % $b;
}

// 4
function mathOperation($a, $b, $operation) {
    switch ($operation) {
        case '+': return add($a, $b);
        case '-': return sub($a, $b);
        case '*': return mul($a, $b);
        case '%': return rem($a, $b);
    }
}
header('Content-Type: text/plain');
echo mathOperation(5, 3, '+') . "\n";
echo mathOperation(5, 3, '-') . "\n";
echo mathOperation(5, 3, '*') . "\n";
echo mathOperation(5, 3, '%') . "\n";