input: Write a python function to return the sum and product of two numbers.
  assert sum_and_product(2, 3) == (5, 6)
  assert sum_and_product(4, 5) == (9, 20)
  assert sum_and_product(0, 10) == (10, 0)
output: def sum_and_product(a, b):
      return (a + b, a * b)