AS Physics: MomentWatch
The torque of the couple due to A and B can be given by the force x distance between them = 1.2 x 2r =2.4r
You can then go on to calculate the next question using this resultant torque as the clockwise moment about the pin, and the component of the other force perpendicular to the pin as the anticlockwise moment.
6cos(theta) x r/2 = 2.4r, giving theta = 36.9 degrees
And then the magnitude of the force on the pin will be the force which is not balanced by a moment, which is 6sin(36.9) = 3.6N