input: Write a python function to calculate the area of a Rectangle class.
  assert Rectangle(4, 5).calculate_area() == 20
  assert Rectangle(6, 7).calculate_area() == 42
  assert Rectangle(10, 10).calculate_area() == 100
output: class Rectangle:
      def __init__(self, width, height):
          self.width = width
          self.height = height
  
      def calculate_area(self):
          return self.width * self.height