A lift goes up with 10 m/s. a pulley P is fixed to the ceiling of the lift. To this pulley other two pulley `P_(1)` and `P_(2)` are attached. `P_(1)` moves up with velocity 30 m/s. A moves up with velocity 10 m/s. D is moving downwards with velocity 10 m/s at same instant of time. Find the velocity of B and that of C at that instant. Assume that all velocities are relative to the ground.