input: Write a function to calculate the area of a triangle given its base and height.
  assert area_of_triangle(5, 4) == 10.0
  assert area_of_triangle(10, 2) == 10.0
  assert area_of_triangle(6, 3) == 9.0
output: def area_of_triangle(base, height):
      return 0.5 * base * height