Butterfly spread. An investor, following this strategy buys a call option with strike price K1, buys another call option with strike price Kz > K1 and sells two call options with strike price K2 = }(K1 + K3). All options are of European type, written on the same stock, and have the same maturity time T. Calculate and sketch the graph of the terminal payoff as a function of the terminal value x = St