a. Suppose that a stock has current price of $15. It is expected that in 4 months, the value of the stock would either be $20 or $13. A 4 months call option with strike price of $17 on the stock is being initiated today. If the interest rates are 5% per annum for 4 months continuously compounded then, what is the price of the call option today? b. What is the price of the option if its a 4 months put option with strike price $18?