1. The problem statement, all variables and given/known data Mastering physics problem 23.76 difficulty rating: two bars=difficult A 2.0-cm-tall object is placed in front of a mirror. A 1.0-cm-tall upright image is formed behind the mirror, 180cm from the object. What is the focal length of the mirror? 2. Relevant equations hi / di = ho / do Thin lens equation 1/o + 1/i = 1/f 3. The attempt at a solution I made a previous attempt but I know why that was wrong. However, if I can see that the object is 2.0cm high and then its image is 1.0cm high. Does that imply that the distance of the object to the mirror is 180cm times 2 = 360cm so its image is 540cm from the mirror. I understand I can use the height ratio to find the magnification. I just cannot see how I can find the obj distance or image distance. I still have 1/o + 1/i = 1/f and it is impossible to solve this equation when I still have three unkowns.