Question 4 (11 marks) Part A: (5 marks) Consider the following two strategies: Strategy A: Long a call option with X: = $20; write two call options, each with X2 = $30; and long a call option with X3 = $40 Strategy B: Long a put option with X1 = $20; write two put options, each with X2 = $30; and long a put option with X3 = $40 All the options have the same maturity and they are used on the same stock. Further assume that the firm pays no dividend. Required: Use ONLY the put-call parity to prove that both strategies A and B have the same cost. You are NOT allowed to use any other methods such as drawing terminal payoff diagram, or setting up terminal payoff table as your proof