Find the total number of students

Problem Description
You are given a 2D array of numbers arr. You have to implement the function matrixSum which will return the sum of all elements of the matrix.

Hint 1: To iterate through 2D arrays, use nested loops.

Hint 2: Iterate through the array and compute the sum of all elements.

Sample Input 1
[[23,48],[12,18]]

Sample Output 1
101

Explanation
Sum of the elements 23 + 48 + 12 + 18 is equal to 101.

Sample Input 2
[[5, 1], [2, 3]]

Sample Output 2
11

Explanation
Sum of the elements 5 + 1 + 2 + 3 is equal to 11.

/**
 * @param {number[][]} arr
 * @return {number}
 */


function matrixSum(arr) {
  // You only need to implement this function.
}

if (matrixSum([[5, 1], [2, 4]]) != 12)
  console.log("Test fails: Expected 12 for input arr = [[5, 1], [2, 4]]");
else
  console.log("Sample test case for input arr = [[5, 1], [2, 4]] passed!");

module.exports = matrixSum