based on the binomial tree model, the expected value of successful outcome with p = 0.6 and n = 20 is 12 (20 * 0.6).  Therefore, there's a total of 12 u and 8 ud.  

Since ud = 1, and u = 1.01, sn = s0 * u^12 = 112.68.  therefore, sn-k = 2.68 thus (sn-k)+ = 2.68
Thus E[(sn-k)+] = 2.68