https://programmers.co.kr/learn/courses/30/lessons/12950
function solution(arr1, arr2) { var answer = []; for(let i = 0; i < arr1.length; i++) { answer[i] = []; for(let j = 0; j < arr1[i].length; j++) { answer[i][j] = arr1[i][j] + arr2[i][j]; } } return answer; }