input: Write a python function to perform basic arithmetic operations using a Calculator class.
  assert c.add(4, 8) == 12
  assert c.subtract(4, 8) == -4
  assert c.multiply(4, 8) == 32
  assert c.divide(4, 8) == 0.5
output: class Calculator:
      def add(self, a, b):
          return a + b
      
      def subtract(self, a, b):
          return a - b
      
      def multiply(self, a, b):
          return a * b
      
      def divide(self, a, b):
          if b == 0:
              raise ValueError("Cannot divide by zero")
          return a / b
  
  c = Calculator()