Lead ball is dropped into lake-how deep is the lake

1. A lead ball is dropped into a lake from a diving board 5.0 mabove the water. After entering the water, it sinks to the bottom with a constant velocity equal to the velocity with which it hit the water. The ball reaches the bottom 3.0 s after it is released.
How deep is the lake?

2. Mary needs to row her boat across a 100 m wide river that is flowing to the east at a speed of 1.0 m/s. Mary can row the boat with a speed of 2.0 m/s relative to the water.
a) If Mary rows straight north, how far down stream will she land?
b) Draw a picture showing Mary's displacement due to rowing, her displacement due to the river's motion, and her net displacement.(If you can)