Two particles P and Q, of masses m kg and 0.3 kg respectively, are at rest on a smooth horizontal plane. P is projected at a speed of 5 m s^-1 directly towards Q. After P and Q collide, P moves with a speed of 2 m s^-1 in the same direction as it was originally moving.

(a) Find, in terms of m, the speed of Q after the collision.

After this collision, Q moves directly towards a third particle R, of mass 0.6 kg, which is at rest on the plane. Q is brought to rest in the collision with R, and R begins to move with a speed of 1.5 m s^-1.

(b) Find the value of m.