Вам просто нужно отслеживать максимум, пока вы вычисляете средние значения:
function findMaxAverage(input) {
let numCompanies = Number(input.shift());
let maxAvg = 0; maxCompany = "";
for (let i = 0; i < numCompanies; i++) {
let company = input.shift();
let passengers = Number(input.shift());
let total = 0;
let count = 0;
while (passengers !== "Finish") {
total += passengers;
count++;
passengers = input.shift();
}
let avg = total / count;
console.log(`${company}: ${Math.floor(avg)} passengers.`);
if (avg > maxAvg) {
maxAvg = avg;
maxCompany = company;
}
}
console.log(`----------`);
console.log(`Maximum: ${maxCompany} with an average of ${Math.floor(maxAvg)} passengers.`);
}
findMaxAverage([2, "Qatar Airways", 95, 231, 323, "Finish", "LOT", 76, 89, 55, "Finish"]);