input: Write a function to perform basic arithmetic 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(a, b):
      return a + b
  
  def subtract(a, b):
      return a - b
  
  def multiply(a, b):
      return a * b
  
  def divide(a, b):
      if b == 0:
          raise ValueError("Cannot divide by zero")
      return a / b