Einstein's theory of relativity tells us we will experience 8 more minutes of gravitation after the dissappearing of the sun. The speed of gravity is c.
Taking a quick look at the picture, I'd say there are two reaction forces: one at the screw and one at the lowest point of the bracket. Both reaction forces have a horizontal and a vertical component, so we have four unknown values. We also have four equations:
1 horizontal force equation...
You can choose the center of torque as you wish.. the result will be the same. It's best to choose the center of torque in a point where a force acts, so this force will cancel out. This simplifies your equations.
And don't forget... there's also a force caused by gravity. You forgot it in...