Answer
$F=210N$
Work Step by Step
The figure below shows that we can turn the distance $0.28m$ into the lever arm by finding the angle to the left of $F$ and change $F$ into a force component $F\cos40$
In other words, the torque produced by force $F$ equals $$\tau=(F\cos40)l$$ $$F=\frac{\tau}{l\cos40}=\frac{45}{0.28\times\cos40}=210N$$
