input: Write a python function to compute the sum of a list of numbers.
  assert sum_numbers([11, 12, 15, 20, 56]) == 110
  assert sum_numbers([1, 2, 3, 4, 5]) == 15
  assert sum_numbers([10, 20, 30]) == 60
output: def sum_numbers(numbers):
      return sum(numbers)