Question

how to solve numericals related to defects of eye?

Answer 1

First you should know about the defects. You can solve such type of numericals as follows:
For myopia,
Object distance, u=infinity
Image distance, v= Far point of person
For hypermetropia,
Object distance, u=-25 cm
Image distance=Near point of defective eye

Then you can use the mirror formula to find focal length.
At last power can be found by using
Power=1/ Focal length (in metres)