A trader creates a long butterfly spread from options with strike prices of $60, $65, and $70 per share by trading a total of 40 option contracts (10 contracts at $60,20 contracts at $65 and 10 contracts at $70). Each contract is written on 100 shares of stock. The options are worth $ 11, $ 14, and $ 18 per share of stock. What is the value of the butterfly spread at maturity as a function of the then stock price? What is the profit of the butterfly spread at maturity as a function of the then stock price