An object 4 cm in size is placed at 25 cm

An object 4 cm in size is placed at 25 cm infront of a concave mirror of focal length 15 cm. At what distance from the mirror should a screen be placed in order to obtain a sharp image ? Find the nature and size of image.

Given that f = -15 cm; u = -25 cm ; ${ H }{ 0 }$ = 4 cm; v = ?
The mirror formula is 1/f = 1/u + 1/v = 1/-15 = 1/-25 + 1/v
1/v = 1/25 - 1/15
1/v = 3-5/ 75 =-2/ 75
v =-37.5 cm
The screen should be placed 37.5 cm from the pole of mirror and the image is real.
Magnification, m = ${ H }
{ i }$ / ho = -v/u = hi / 4 = 37.5 / 25
hi = 37.5 / 25 x 4 = -6 cm
So the image is enlarged and inverted.