❗️Что будет на выходе:

const transactions = [
  { id: 1, type: "credit", amount: 200 },
  { id: 2, type: "debit",  amount: 50  },
  { id: 3, type: "credit", amount: 150 },
  { id: 4, type: "debit",  amount: 30  },
  { id: 5, type: "credit", amount: 100 },
];

const result = transactions
  .filter(tx => tx.type === "credit")
  .map(tx => ({ ...tx, amount: tx.amount * 1.1 }))
  .reduce((acc, tx) => acc + tx.amount, 0);

console.log(result.toFixed(2));

Ответ: 495.00

JavaScript test | #JavaScript