Iterating Over Multidimensional Arrays in PHP

Let's now learn how to iterate over multidimensional arrays using loops. Suppose we have the following array:

<?php
	$arr = [
		['a', 'b', 'c'],
		['d', 'e', 'f'],
		['g', 'h', 'i'],
	];
?>

As you can see, this array is two-dimensional, which means that to iterate through it, two nested foreach loops are needed:

<?php
	foreach ($arr as $sub) {
		foreach ($sub as $elem) {
			echo $elem;
		}
	}
?>

Given the following array:

<?php
	$arr = [[1, 2, 3], [4, 5, 6, 7], [8, 9]];
?>

Using two nested loops, find the sum of the elements of this array.