3.js

function solve(input) {
     let fruit = input.shift();
     let sizeOfSet = input.shift();
     let countOfSets = Number(input.shift());

     let prizePacket = 0;
     let prizeForSets = 0;


     if (sizeOfSet === 'small') {
         switch(fruit) {
             case 'Watermelon':
                 prizePacket = 2 * 56;
                 prizeForSets = countOfSets * prizePacket;
                 break;
            case 'Mango':
                prizePacket = 2 * 36.66;
                prizeForSets = countOfSets * prizePacket;
                break;
            case 'Pineapple':
                prizePacket = 2 * 42.10;
                prizeForSets = countOfSets * prizePacket;
                break;
            case 'Raspberry':
                prizePacket = 2 * 20;
                prizeForSets = countOfSets * prizePacket;
                break;
         }

     } else if (sizeOfSet === 'big') {
        switch(fruit) {
            case 'Watermelon':
                prizePacket = 5 * 28.70;
                prizeForSets = countOfSets * prizePacket;
                break;
           case 'Mango':
               prizePacket = 5 * 19.60;
               prizeForSets = countOfSets * prizePacket;
               break;
           case 'Pineapple':
               prizePacket = 5 * 24.80;
               prizeForSets = countOfSets * prizePacket;
               break;
           case 'Raspberry':
               prizePacket = 5 * 15.20;
               prizeForSets = countOfSets * prizePacket;
               break;
        }

        if (prizeForSets >= 400 && prizeForSets <= 1000) {
            prizeForSets = prizeForSets - prizeForSets * 0.15;

        } else if (prizeForSets > 1000) {
            prizeForSets = prizeForSets - prizeForSets * 0.5;

        }

     }

     console.log(`${prizeForSets.toFixed(2)} lv.`)
}