Safari

function safari(input) {
    let budget = Number(input[0]);
    let fuel = Number(input[1]);
    let day = input[2];

    let sum = fuel * 2.1 + 100;

    if (day == "Saturday") {
        sum *= 0.9;
    } else {
        sum *= 0.8;
    }

    if (budget >= sum) {
        console.log(`Safari time! Money left: ${(budget - sum).toFixed(2)} lv. `);
    } else {
        console.log(`Not enough money! Money needed: ${(sum - budget).toFixed(2)} lv.`);
    }
}

Решение с тернарен оператор:

function safari(input) {
    let budget = Number(input[0]);
    let fuel = Number(input[1]);
    let day = input[2];

    let sum = fuel * 2.1 + 100;
    sum *= day == "Saturday"? 0.9 : 0.8;

    console.log(budget >= sum? `Safari time! Money left: ${(budget - sum).toFixed(2)} lv. `
                :`Not enough money! Money needed: ${(sum - budget).toFixed(2)} lv.`);
}

Тарикатско решение:)

function safari(input) {
    let sum = Number(input[0]) - ((Number(input[1]) * 2.1 + 100) * (input[2] == "Saturday" ? 0.9 : 0.8));
    console.log(sum >= 0 ? `Safari time! Money left: ${sum.toFixed(2)} lv. `
                :`Not enough money! Money needed: ${Math.abs(sum).toFixed(2)} lv.`);
}