A man stands 10m in front of a large plane mirror. So, how far must he walk before
he is 5m away from his image?

Dear student

In a plane mirror, object distance = Image distance

Given Man's distance from image is to be 5 m.

This means distance of man from mirror + Distance of image from mirror = 5 m

2 x  (Distance of man from mirror) = 5 m 

Distance of man from mirror = 2.5 m

Initially he is 10 meters from the mirror.

So, he will have to walk (10-2.5)  = 7.5 meters towards the mirror.

With regards