void main() async {
  final square3Future = square(3);
  final square4Future = square(4);
  final square3 = await square3Future;
  final square4 = await square4Future;
  int sum = square3 + square4;
  print('3^2 + 4^2 = $sum');
}

Future<int> square(int val) async {
  print('${DateTime.now()} started calculating $val^2');
  await Future.delayed(Duration(seconds: 1));
  int result = val * val;
  print('${DateTime.now()} finished calculating $val^2');
  return result;
}