input: Write a function to add a specified mark to each value in a list of marks. The function should take two parameters: marks (a list of integers) and mark (an integer). If the list of 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([], 4)==[]
output: def add_marks(marks, mark):
      if not marks:
          return []
      return [x + mark for x in marks]