looking at the top view of a door that is 1.68 m wide, Two forces are applied to the door.

Hinge, angle a is at halfway point, pointing up and right 55 degrees, Angle b is at edge pointing down and left 55 degrees.
Both forces at the angles are 12N

My crappy illustration:

0----------/a----------/b

What is the magnitude of the net torque on the door with respect to the hinge?

I thought since they are pulling opposite directions they would be:
net torque=Fa(la)-Fb(lb)
torque of a minus torque of b, (or vice versa) but apparently my answer is wrong.
I've tried several other ways, but none with an answer that matches one of these.

I have 5 choices:
0Nm
4.4Nm
8.3Nm
9.1Nm
11Nm

Help please?

Edit: forgot my forces!

Hi H,
I think you have it right, but you must have calculated something wrong.
Fa(La) - Fb(Lb) = 12(sin55)(1.68) - 12(sin55)(0.86) = 8.3Nm.
Peace,
Ron