An observer is sitting $20 \mathrm{~cm}$ away from a circular convex mirror, with his eyes on the axis of the mirror. The mirror has diameter of $6 \mathrm{~cm}$ and focal length $30 \mathrm{~cm}$ is fixed with its principal axis horizontal. The image is formed at distance $12 \mathrm{~cm}$ from the mirror and the distance of mid-point of diameter from the pole is $0.75 \mathrm{~cm}$. The angular field of view in the horizontal plane seen in the mirror by the observer is :
(a) $\tan \theta=0.5672$
(b) $\tan =0.3014$
(c) $\tan \theta=0.5279$
(d) $\tan \theta=0.2516$