Family Trip

function familyTrip(input) {
    let budget = Number(input[0]);
    let overnight = Number(input[1]);
    let overnightPrice = Number(input[2]);
    let additionalCosts = Number(input[3]);

    if (overnight > 7) {
        overnightPrice *= 0.95;
    }

    let totalPrice = overnight * overnightPrice + additionalCosts * budget / 100;

    if (totalPrice > budget) {
        console.log(`${(totalPrice - budget).toFixed(2)} leva needed.`);
    } else {
        console.log(`Ivanovi will be left with ${(budget - totalPrice).toFixed(2)} leva after vacation.`);
    }
}

РЕШЕНИЕ С ТЕРНАРЕН ОПЕРАТОР:

function familyTrip(input) {
    let budget = Number(input[0]);
    let overnight = Number(input[1]);
    let overnightPrice = Number(input[2]);
    let additionalCosts = Number(input[3]);

    budget -= overnight * (overnight > 7 ? 0.95 : 1) * overnightPrice + (additionalCosts * budget) / 100;

    console.log(
        budget < 0 ?
        `${Math.abs(budget).toFixed(2)} leva needed.` :
        `Ivanovi will be left with ${budget.toFixed(2)} leva after vacation.`
    );
}