input: Write a 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 and return the modified list.
  assert add_marks([87, 56, 99, 54], 4) == [91, 60, 103, 58]
  assert add_marks([34, 45, 67], 10) == [44, 55, 77]
  assert add_marks([100, 90, 80], -20) == [80, 70, 60]
  assert add_marks([], 5) == []
  assert add_marks([2, 4, 6], 0) == [2, 4, 6]
output: def add_marks(marks, mark):
      return [x + mark for x in marks]