I've almost done but not sure whether im doing it right. would like to compare and contrast. Thank you.

(b) A trader creates a long butterfly spread from options with strike prices $60, $65, and $70 by trading a total of 400 options. The options are worth $11, $14, and $18. What is the maximum net loss (after the cost of the options is taken into account)? Explain your answer in detail.