input: Write a function to sum a list of numbers.
  assert sum_of_numbers([2, 4, 6, 8, 10]) == 30
  assert sum_of_numbers([1, 2, 3, 4, 5]) == 15
  assert sum_of_numbers([10, 20, 30]) == 60
output: def sum_of_numbers(numbers):
      return sum(numbers)