input: Write a function that adds a given integer to each element of a list and returns a new list with the modified elements. The function should be called add_marks, which takes two parameters: marks (a list) and mark (an integer). If marks is empty, the function should return an empty list.
  assert add_marks([87, 56, 99, 54], 4) == [91, 60, 103, 58]
  assert add_marks([10, 20, 30], 5) == [15, 25, 35]
  assert add_marks([], 3) == []
  assert add_marks([70], 0) == [70]
  assert add_marks([5, 10, 15, 20], -5) == [0, 5, 10, 15]
output: def add_marks(marks, mark):
      return [x + mark for x in marks] if marks else []