input: Write a python function to calculate the sum and average of a given list.
  assert sum_and_average([1,2,3,4,5]) == (15, 3.0)
  assert sum_and_average([10,20,30,40,50]) == (150, 30.0)
  assert sum_and_average([5,10,15,20,25]) == (75, 15.0)
output: def sum_and_average(lst):
      total = sum(lst)
      average = total / len(lst)
      return total, average