Hel please!! :c A ball with a mass of .012 kg moving at 15.0 m/s collides with a second ball with a mass of 36 g moving at 5.0 m/s. After the collision, the 12 g ball moves in the same direction at 6.0 m/s. What is the resulting velocity of the 36 g ball?

Alead ball is dropped into a lake from a diving board 5m above the water . it hits the water with a certain velocity and then sink with constant velocity in bottom . it reaches the bottom 5 second after it is dropped if g= 10m/s2 . find depth of the lake and average velocity of the ball ?