1. The problem statement, all variables and given/known data The image of a tree just covers the length of a plane mirror 3.80 cm tall when the mirror is held 40.0 cm from the eye. The tree is 20.0 m from the mirror. What is the height of the tree? 2. Relevant equations m=y'/y, s=s'=20m (from problem statement) 3. The attempt at a solution At first I simply thought the height of the image in the plane mirror is equal to the height of the object, this however is incorrect. Where I am puzzled is how to factor in the distance of the observer from the mirror, and how the object height can be different from the image height when lateral magnification in a plane mirror=1. Any suggestions on how to begin this problem are greatly appreciated, geometric optics are proving to be quite difficult for me to grasp.