day 42

let avgWaitTime = function (customers) {
    let total = 0;
    let end = 0;
    for (let i = 0; i < customers.length; i++) {
        end = Math.max(end + customers[i][1], customers[i][0] + customers[i][1]);
        total += end - customers[i][0];
    }
    return (total / customers.length).toFixed(5);
};