input: Write a function to create a basic calculator with operations add, subtract, multiply, and divide.
  assert add(10, 5) == 15
  assert subtract(10, 5) == 5
  assert multiply(10, 5) == 50
  assert divide(10, 5) == 2.0
output: def add(x, y):
      return x + y
  
  def subtract(x, y):
      return x - y
  
  def multiply(x, y):
      return x * y
  
  def divide(x, y):
      if y == 0:
          raise ValueError("Cannot divide by zero")
      return x / y