<?php declare(strict_types=1); // strict requirement
function sum(int $x,
int $y) {
    $z = $x + $y;
    return $z;
}


echo "5 + 10 = " . sum(5, 10) . "<br>";
echo "7 + 13 = " . sum(7, 13) . "<br>";
echo "2 + 4 = " . sum(2, 4);
?>