Given the displacement vector D = (4î − 8ĵ) m, find the displacement vector R (in m) so that D + R = −3Dĵ. (Express your answer in vector form.)

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 ?