Mirrors physics question?

Question

What is the focal length of a makeup mirror that produces a magnification of 1.50 when a person's face is 12.0 cm away?

Answer 1

The location of the image is:

q = - Mp = - 1.50 x 0.120 m = - 0.180 m

The focal length is:

f = 1 / ((1 / p) + (1 / q))

= 1 / ((1 / 0.120 m) + (1 / - 0.180 m))

= 0.360 m