Refraction at a concave interface

A concave interface is defined by a circle with a center $C$ at $(x_c=0,y_c=0)$ and a radius $R=$  cm. A light ray emitted from position $o$ $(x_0=$ , $y_0=$ $)$ cm strikes this interface at point $P$ at a height $y_p=$  cm. The index of refraction is $n_1=1$ to the left of the interface and $n_2=$  to the right of the interface. What is the angle between the normal to the interface at point $P$ (the gray line that runs through $C$ and $P$) and the refracted ray?