const radiusArray = [20, 40, 60];

console.info("Generating area array using regular method");
const areaArray = [];
for (let i = 0; i < radiusArray.length; i++) {
  areaArray.push(Math.floor(Math.PI * radiusArray[i] * radiusArray[i]));
}

console.log(areaArray);

console.info("Generating area array using array.map()");
const areaArrayWithMap = radiusArray.map((radius) => {
  return Math.floor(Math.PI * radius * radius);
});

console.log(areaArrayWithMap);