For an American put option on a stock with 6 months to expiry: (i) The strike price is 40 . (ii) The price of a European call option with 6 months to expiry and strike price 40 is 0.80. (iii) The stock pays a dividend of x at the end of 4 months. (iv) The continuously compounded risk-free interest rate is 0.06. Determine the least upper bound of values of x for which it may be optimal to exercise the option immediately