Question

A concave mirror of focal length 10cm is placed at a distance of35 cmfrom a wall. How far from the wall an object be placed so that its image formed by the mirror falls on the wall

Answer 1

for concave mirror f= -10
dist. of image=v= -35
by using mirror formula
1/f = 1/v + 1/u

Answer 2

the object should be placed at a distance of 14cm in front of lens

I. e u=-14cm

Hope it will help