PHP program that multiplies corresponding elements of two given lists

<?php

function multiply_two_lists($x, $y)

 {

    $a = explode(' ',trim($x));

    $b = explode(' ',trim($y));

    foreach($a as $key=>$value) 

 {

        $output[$key] = $a[$key]*$b[$key];

  }

    return implode(' ',$output);

 }

echo multiply_two_lists(("10 12 3"), ("1 3 3"))."\n";

?>