Trigonometry · Superchallenge problem

Wheel $A$ (radius $5$ cm) is joined by a belt to wheel $B$ (radius $8$ cm). Wheel $B$ shares an axle with wheel $C$ (radius $3$ cm), which is belted to wheel $D$ (radius $12$ cm). If $A$ turns at $120$ RPM, find the angular speed of $D$ in RPM.