520 cm tall pencil is placed 110 cm in front of a mirror An

5.20- cm tall pencil is placed 11.0 cm in front of a mirror. An image is formed 4.30 cm behind the mirror. What is the focal length of the mirror?

Using the Lens equation:

1/v + 1/u = 1/f

where v = image distance = 4.3 cm

u = image distance = -11 cm

f = focal length

So,

1/4.3 + 1/-11 = 1/f

So, f = 7.06 cm <-------answer