input: Write a function to create a Python function called add_marks which takes two parameters: marks(a list) and mark(an integer). The function should add the mark to each value in the marks list. If the marks list is empty, the function should return an empty list.
  assert add_marks([87, 56, 99, 54], 4) == [91, 60, 103, 58]
  assert add_marks([], 4) == []
  assert add_marks([1, 2, 3], 0) == [1, 2, 3]
  assert add_marks([10, 20, 30], -5) == [5, 15, 25]
  assert add_marks([3, 5, 7, 9], 2) == [5, 7, 9, 11]
output: def add_marks(marks, mark):
      if not marks:
          return []
      return [x + mark for x in marks]