Forces and equilibrium — practice question

A small smooth ring $R$, with mass $0.2\,\text{kg}$, is placed on a light inextensible string $ARB$. The two ends of the string are fixed at points $A$ and $B$ on a roof sloping at $45^\circ$ to the horizontal. A horizontal force of magnitude $P\,\text{N}$, acting in the plane $ARB$, is exerted on the ring. The section $BR$ of the string is perpendicular to the roof, and the section $AR$ makes an angle of $70^\circ$ with the horizontal (see diagram). The system is in equilibrium.