input: Write a function to add a given integer mark to each element in a list of marks. If the list is empty, return the empty list.
  assert add_marks([87, 56, 99, 54], 4)==[91, 60, 103, 58]
  assert add_marks([], 4)==[]
  assert add_marks([78, 34, 92], 7)==[85, 41, 99]
  assert add_marks([65, 72, 88], 0)==[65, 72, 88]
  assert add_marks([45], 15)==[60]
output: def add_marks(marks, mark_to_add):
      return [mark + mark_to_add for mark in marks]