My method:- I have tried many ways but i did not get any answer so i used a scale and a compass and constructed the circle and took angle to be $Tan^{-1}(4/3)$ in a circle of radius 2 units and got the answer to be $0.5$ but the actual answer is D
Please help me
Hint:
From the construction, if $H$ is the orthogonal projection of $F$ on $OA$, we have $\overline{HF}=\frac{1}{2}\overline {DB}$, so: $$ \frac {\overline{HF}}{d}=\frac{\frac{1}{2}\overline{DB}}{d}=\frac{1}{2}\sin \theta = \sin \alpha $$ where $\alpha$ is the arc $AF$. and $\theta$ is the arc $AB$ (see the figure)
So : $\alpha=\sin^{-1}\left(\frac{1}{2}\sin \theta \right)$