input: Write a function to calculate the area of a triangle using its base and height.
  assert area_of_triangle(10, 5) == 25.0
  assert area_of_triangle(7, 3) == 10.5
  assert area_of_triangle(0, 5) == 0.0
output: def area_of_triangle(base, height):
      return 0.5 * base * height