4. Let W(t), W2(t) be two independent standard Brownian motions, starting at zero. Viewing (W,),W2)),t a random walk on the x-y plane starting at the origin, calculate the probability that the random walk never crosses the line xty-1 for 0 Sts 3. (see figure) xty-1 Hint: show that Z(t)-W) equal to 1) and use this. W2(t) is a 1-dimensional BM (with variance not necessarily