Could you help giving me explanations on this problem ? Thank you.

_- ' A stock price is currently at 5'0 = $50. Over each of the next two year periods it is expected to go up by 10% p. a. or down by 10% p. a. The risk-free interest rate is 1% p. a. with continuous compounding. Use a two-step binomial tree model to compute today's arbitrage-free price of a European-style Asian Forward Start Coil Option with maturity in two years (T = 2). This option pays the holder the payoff 2 + 1 i=0 at maturity T = 2, where 31 denotes the price of the stock in one year and 32 denotes the price of the stock in two years