input: Write a python function to calculate the surface area and volume of a sphere given its radius.
  assert sphere_surfacearea(1) == 12.566370614359172
  assert sphere_surfacearea(0) == 0
  assert sphere_surfacearea(2.5) == 78.53981633974483
  assert sphere_volume(1) == 4.1887902047863905
  assert sphere_volume(0) == 0
  assert sphere_volume(2.5) == 65.44984694978735
output: import math
  
  def sphere_surfacearea(radius):
      return 4 * math.pi * radius ** 2
  
  def sphere_volume(radius):
      return (4/3) * math.pi * radius ** 3