A light ray moves from air into a convex glass surface of radius of

curvature $15\mathrm{.}0mm$ and index of refraction $1\mathrm{.}6.$ The ray emerges from

the optical axis $45mm$ before the curved glass surface.

$($a$)$ Sketch the surface, incident and refracted rays and optical axis.

$($b$)$ How far from the surface $($in $mm)$ does the light ray cross the

optical axis inside the glass?