A stock price is currently $50. It is known that at the end of one year it will be either $40 and $60. The exercise price of a one-year European call option is $55. The risk-free interest rate is 5% per annum. Construct a binoamial tree to show the payoff of the call option at the expiration date. (5%) Based on the binomial tree model, what is the value of the call option? (15%) Address the relation between the binomial tree model and the Black-Scholes model. (5%)