AP EAPCET 08-Jul-2022 Shift 2 Paper

We can given with following arrangement :

From diagram it is clear that focus of lens 1 , point F1 must be focus of lens 2 also.
In this way, a parallel beam, of light becomes again parallel after passing through system of lenses.
Hence, distance F2L2,
F2L2=15+40=55‌cm
So, focal length of convex lens is 55‌cm.