iteration.js

function multy(arr) {
    let result = 0;
    arr.map(arr2 => {
        result += arr2.reduce((acc, cur) => {
            return acc != 0 ? acc = acc * cur : acc = cur
        },0)
    });
    return result;
}
const arr = [[5, 6, 4], [2, 3], [1, 2]];
console.log(multy(arr));