For a given optical system, the principal axis is x-axis and coordinates of object are `(-30,+1,0)` and coordinates of image are `(+20,-2,0)` All coordinates are in cm.
If the optical system is a spherical refracting surface, its centre of curvature is at what point?
A. `-15` cm
B. `+25` cm
C. `(-40)/3` cm
D. `-80` cm