input: Write a function to validate a billing address.
  assert validate_billing_address("123 Main St\nSpringfield, IL 62704") == True
  assert validate_billing_address("123 Main St\nSpringfield, IL") == False
  assert validate_billing_address("123 Main St\nSpringfield, IL 6270a") == False
  assert validate_billing_address("\nSpringfield, IL 62704") == False
output: def validate_billing_address(address):
      import re
      pattern = r'^\d+ .+\n.+, [A-Z]{2} \d{5}$'
      return bool(re.match(pattern, address))