100 lb boy stands at one edge of the skating board. The board is 6 ft long and weighs 60 lb. Initially, the boy and the board are at rest. The boy then walks 6 ft to the opposite end with a constant speed of 3 ft/s relative to the board. Neglect friction between the board and the ground. 

Find: 

(a) Speed of the board

(b) Displacement of the board  just as the boy is about to step off.