const addNumbers = [3,5,9,1,2].myNewReducer((acc, num) => acc + num, 0);
console.log(addNumbers); // 20

const averageSalaryGainPerYear = developers.myNewReducer(([tSal, tExp], data) => {
    tSal = tSal + data.salary;
    tExp = tExp + data.expInYears;
    return [tSal, tExp];
}, [0,0]);

const [ tSalaryAmount, tExperinceYears ] = averageSalaryGainPerYear;
const averageGainPerYear = Math.floor(tSalaryAmount / tExperinceYears);

console.log(averageGainPerYear); // 25833