A Cell Phone That Is $8.90 \mathrm {~cm}$ Tall Is Placed in Front of a Convex Mirror

Multiple Choice

A cell phone that is $8.90 \mathrm {~cm}$ tall is placed in front of a convex mirror. The image of the phone is $7.80 \mathrm {~cm}$ tall and is located $14.8 \mathrm {~cm}$ from a mirror. What is the mirror's focal length?

A) $+ 120 \mathrm {~cm}$
B) $- 105 \mathrm {~cm}$
C) $- 120 \mathrm {~cm}$
D) $+ 16.9 \mathrm {~cm}$
E) $- 13.0 \mathrm {~cm}$