Mobile Operator

function mobileOperator(input) {
    let year = input[0];
    let type = input[1];
    let net = input[2];
    let month = Number(input[3]);

    let sum = 0;

    switch (type) {
        case "Small":
            if (year === "one") {
                sum = 9.98;
            } else {
                sum = 8.58;
            }
            break;

        case "Middle":
            if (year === "one") {
                sum = 18.99;
            } else {
                sum = 17.09;
            }
            break;

        case "Large":
            if (year === "one") {
                sum = 25.98;
            } else {
                sum = 23.59;
            }
            break;

        case "ExtraLarge":
            if (year === "one") {
                sum = 35.99;
            } else {
                sum = 31.79;
            }
            break;
    }

    if (net === "yes") {
        if (sum <= 10) {
            sum += 5.5;
        } else if (sum > 10 && sum <= 30) {
            sum += 4.35;
        } else {
            sum += 3.85;
        }
    }

    let total = sum * month;

    if (year === "two") {
        total -= 3.75 * total / 100;
    }
    console.log(`${total.toFixed(2)} lv.`);
    return;
}


РЕШЕНИЕ СЪС SWITCH И ТЕРНАРЕН ОПЕРАТОР:

function mobileOperator(input) {
    let year = input[0];
    let type = input[1];
    let net = input[2];
    let month = Number(input[3]);

    let sum = 0;

    switch (type) {
        case "Small":
            sum = year === "one" ? 9.98 : 8.58;
            break;

        case "Middle":
            sum = year === "one" ? 18.99 : 17.09;
            break;

        case "Large":
            sum = year === "one" ? 25.98 : 23.59;
            break;

        case "ExtraLarge":
            sum = year === "one" ? 35.99 : 31.79;
            break;
    }

    sum += net === "yes" ? (sum <= 10 ? 5.5 : sum > 30 ? 3.85 : 4.35) : 0;

    let total = sum * month;
    total -= year === "two" ? 3.75 * total / 100 : 0;

    console.log(`${total.toFixed(2)} lv.`);
    return;
}


РЕШЕНИЕ С ТЕРНАРЕН ОПЕРАТОР:

function mobileOperator(input) {
    let year = input[0];
    let type = input[1];
    let net = input[2];
    let month = Number(input[3]);

    let sum = (type === "Small" ? (year === "one" ? 9.98 : 8.58)
            : type === "Middle" ? (year === "one" ? 18.99 : 17.09)
            : type === "Large" ? (year === "one" ? 25.98 : 23.59)
            : type === "ExtraLarge" ? (year === "one" ? 35.99 : 31.79) : 0);

    sum += net === "yes" ? (sum <= 10 ? 5.5 : sum > 30 ? 3.85 : 4.35) : 0;

    let total = sum * month;
    total -= year === "two" ? 3.75 * total / 100 : 0;

    console.log(`${total.toFixed(2)} lv.`);
    return;
}