Hi i am revising, exams in 2 week and i got stuck on this question

A light inextensible string hsa its e4nds attached to 2 fixed points A and B.... With A vertically above B, smooth ring, R of mass 0.8Kg is treaded on the string and is pulled by a horizontal force of magnitude x newton...The ring rests in equilibrium...

http://img59.imageshack.us/img59/5993/maths.png
Find tension in the string <<< What am i suppsed to find, what tension exactly ?

Value of X

I can work the triangles

by vectors, or trigonometry, i just dont know what to look for ?