DC Motor: Rotating Coil in Magnetic Field

[Ry122]

The diagram shows a DC electric motor containing a rectangular coil of 20 turns and of length .50m and width .40m The coil is pivoted so that it can rotate freely on an axle. The coil is shown lying horizontally in a magnetic field of uniform stength .60T. A current of 3.5A is passing through the coil in the direction PQRS.
Im totally lost with this one. Don't know where to start.

 

[DAKONG]

find couple moment?