What is the net torque on a pivoted metal plate due to three forces?

[mvpshaq32]

Homework Statement

A square metal plate 0.180m on each side is pivoted about an axis through point O at its center and perpendicular to the plate. Calculate the net torque about this axis due to the three forces shown in the figure if the magnitudes of the forces are F₁ = 18.0 N, F₂ = 17.0 N, and F₃ = 14.6 N. The plate and all forces are in the plane of the page. Take positive torques to be counterclockwise.

http://session.masteringphysics.com/problemAsset/1039975/3/yf_Figure_10_40.jpg

Homework Equations

Torque=Frsin(x)

The Attempt at a Solution

I tried to solve this problem by adding 0.09[-Torque₁ + Torque₂ + Torque₃ sin(45)], giving me an answer of 0.839 which was the not right and then I tried using half the length of the diagonal of the square as the radius which was 0.127, giving me a net torque of 1.19 which was also wrong. How do I do this problem then?

 

[rl.bhat]

Check the torque 3. F3 is perpendicular to the diagonal through O.