input: Write a python function to calculate the area of a rectangle using the Rectangle class.
  assert Rectangle(4, 5).get_area() == 20
  assert Rectangle(10, 2).get_area() == 20
  assert Rectangle(3, 7).get_area() == 21
output: class Rectangle:
      def __init__(self, width, height):
          self.width = width
          self.height = height
  
      def get_area(self):
          return self.width * self.height