Two solutions from other collegues (you can find them with the search button using "Food for Pets"):

function footFotPets(input) {
    let days = Number(input[0]);
    let totalFoot = Number(input[1]);
    let sumDogFoot = 0;
    let sumCatFoot = 0;
    let totalEatenFoot = 0;
    let totalPercent = 0;
    let sumBisscuits = 0;
    let totalDogPercents = 0;
    let totalCatPercents = 0;
    let counter = 2;

    for (let i = 1; i <= days; i++) {

        let dogFoot = Number(input[counter++]);
        let catFoot = Number(input[counter++]);

        sumDogFoot += dogFoot;
        sumCatFoot += catFoot;

        if (i % 3 == 0) {
            let currentSumBisscuits = (dogFoot + catFoot) * 0.10;
            sumBisscuits += currentSumBisscuits;
        }
    }

    totalEatenFoot = sumDogFoot + sumCatFoot;
    totalDogPercents = (sumDogFoot / totalEatenFoot) * 100;
    totalCatPercents = (sumCatFoot / totalEatenFoot) * 100;

    totalPercent = (totalEatenFoot / totalFoot) * 100;

    console.log(`Total eaten biscuits: ${Math.round(sumBisscuits)}gr.`);
    console.log(`${totalPercent.toFixed(2)}% of the food has been eaten.`);
    console.log(`${totalDogPercents.toFixed(2)}% eaten from the dog.`);
} 

function petFood(input) {
  let days = Number(input.shift());
  let totalFood = Number(input.shift());
  let dogFood = 0;
  let catFood = 0;
  let counter = 0;
  let bonus = 0;

  for (let i = 1; i <= days; i++) {
    let Dogsfood = Number(input.shift());
    dogFood += Dogsfood;
    let Catsfood = Number(input.shift());
    catFood += Catsfood;

    counter++;

    if (counter % 3 ===0) {
      bonus += (Dogsfood + Catsfood) * 0.1;
    }
  }
  
  bonus = Math.round(bonus);
  
  console.log(`Total eaten biscuits: ${bonus}gr.`);
  console.log(`${(((dogFood + catFood) / totalFood) * 100).toFixed(2)}% of the food has been eaten.`);
  console.log(`${((dogFood / (dogFood + catFood)) * 100).toFixed(2)}% eaten from the dog.`);
  console.log(`${((catFood / (dogFood + catFood)) * 100).toFixed(2)}% eaten from the cat.`);
}