A trader creates a long butterfly spread from options with strike prices of $60, $65, and $70 per share by trading a total of 60 option contracts (15 contracts at $60, 30 contracts at $65 and 15 contracts at $70). Each contract is written on 100 shares of stock.The options are worth $12, $14.5, and $19 per share of stock. Derive the profit of this position at maturity as a function of the then spot price.