5. Suppose you are tossing a fair coin to bet. At each time your gain is Xi. The rule is: (i) if you get heads at i-th toss, Xi = 1$; (ii) if you get tails at i-th toss, Xi = -1$. Let Wn = X1 + X2+ . .. + Xn with Wo = 0. Note that Wn represents your total wealth after n tosses. Suppose after 100 tosses you have 11$, that is W100 = 11. What is your expected wealth if you do another 100 tosses, that is E [W200 | W100 = 11]