Exercise 4.3. In the three-period model of Figure 1.2.2 of Chapter 1, let the interest rate be r = iso the risk-neutral probabilities are p = q = 1. Find the time-zero price and optimal exercise policy (optimal stopping time) for the path-dependent American derivative security whose intrinsic value at each 116 4 American Derivative Securities + time n, n = 0, 1, 2, 3. is (4 - nti L-, S;). This intrinsic value is a put on the average stock price between time zero and time n. Exercise 4.3. In the three-period model of Figure 1.2.2 of Chapter 1, let the interest rate be r = iso the risk-neutral probabilities are p = q = 1. Find the time-zero price and optimal exercise policy (optimal stopping time) for the path-dependent American derivative security whose intrinsic value at each 116 4 American Derivative Securities + time n, n = 0, 1, 2, 3. is (4 - nti L-, S;). This intrinsic value is a put on the average stock price between time zero and time n