1. The problem statement, all variables and given/known data The distance between an object and its image is fixed at 40.0 cm. A converging lens of focal length f = 4.2 cm forms a sharp image for two positions of the lens. What is the distance a between these two positions? 2. Relevant equations 1/p + 1/q = 1/f 3. The attempt at a solution I am very confused with this problem and really have no idea where to begin. If anyone can provide some assistance, that would be great. Thanks.