Мой вариант решения:
let getStatistics = function (players) {
let goalsAll = 0;
for (let i = 0; i <= players.length-1; i++) {
goalsAll += players[i].goals;
}
for (let i = 0; i <= players.length-1; i++) {
players[i].coefficient = players[i].goals * 2 + players[i].passes;
players[i].percent = Math.round((players[i].goals * 100) / goalsAll);
}
return players;
};