Problem 4. A woman can row a boat at 6.4km/h in still water. (a) If she is crossing a river where the current is 3.2km/h, in what direction must her boat be headed if she wants to reach a point directly opposite her starting point? (b) If the river is 6.4km wide, how long will she take to cross the river? (c) Suppose that instead of crossing the river she rows 3.2km down the river and then back to her starting point. How long will she take? (d) How long will she take to row 3.2 km up the river and then back to her starting point? (e) In what direction should she head the boat if she wants to cross in the shortest possible time, and what is that time