Convex mirror. PLEASE HELP!! 1. The problem statement, all variables and given/known data An object 30 cm tall is placed 20 cm in front of a convex mirror. If the height of the image is +10 cm, find the focal lenght of the mirror. 2. Relevant equations 3. The attempt at a solution I know to use 1/f = -(Image distance from V) / Object distance from V. But, now they tell me how tall they are. How to solve now?