input: Write a function to add a given integer mark to each value in a list of marks. If the input list is empty, return an empty list. The function should be named add_marks and should take two parameters: marks (a list) and mark (an integer).
  assert add_marks([87, 56, 99, 54], 4)==[91, 60, 103, 58]
  assert add_marks([], 4)==[]
output: def add_marks(marks, mark):
      return [x + mark for x in marks]