Accumulating Array Elements in PHP Loops

Let's use a loop to find the sum of the array elements:

<?php
	$arr = [1, 2, 3, 4, 5];
	$res = 0;
	
	foreach ($arr as $elem) {
		$res += $elem;
	}
	
	echo $res;
?>

Given an array:

<?php
	$arr = [2, 5, 9, 3, 1, 4];
?>

Find the sum of the elements of this array.

Given an array:

<?php
	$arr = [2, 5, 9, 3, 1, 4];
?>

Find the sum of the elements that are even numbers.

Given an array:

<?php
	$arr = [2, 5, 9, 3, 1, 4];
?>

Find the sum of the squares of the elements of this array.

Given an array:

<?php
	$arr = [2, 5, 9, 3, 1, 4];
?>

Find the product of the elements of this array.