a) A butterfly spread is the purchase of one call at exercise price X1, the sale of two calls at exercise price X2, and the purchase of one call at exercise price X3. X1 is less than X2, and X2 is less than X3 by equal amounts, and all calls have the same expiration date. Write down the payoff function to this strategy and graph it. b) A vertical combination is the purchase of a call with exercise price X2 and a put with exercise 1 price X1, with X2 greater than X1. Write down the payoff function to this strategy and graph it.