5. Consider the binomial stock price model with T = 4, So = 20, u = 1.2214 and d = 1/u = 0.8187. The interest rate is r = 3.82%. There is a American-type put option with maturity time T 4 and strike price E 20. Is it optimal to exercise this American-type put option early? If so, under what circumstances (when and where)? 5. Consider the binomial stock price model with T = 4, So = 20, u = 1.2214 and d = 1/u = 0.8187. The interest rate is r = 3.82%. There is a American-type put option with maturity time T 4 and strike price E 20. Is it optimal to exercise this American-type put option early? If so, under what circumstances (when and where)