input: Write a python function to calculate the sum and average of a list of numbers.
  assert sum_and_avg([5, 9, 16, 17]) == (47, 11.75)
  assert sum_and_avg([10, 20, 30, 40]) == (100, 25.0)
  assert sum_and_avg([1, 2, 3, 4]) == (10, 2.5)
output: def sum_and_avg(numbers):
      total = sum(numbers)
      average = total / len(numbers)
      return total, average