1. The problem statement, all variables and given/known data http://img368.imageshack.us/img368/9489/physicszv8.jpg [Broken] 2. Relevant equations (1/f) = (1/p) + (1/q) 3. The attempt at a solution I tried solving this but I don't know what the original P was so I can't solve for q. How can I solve this?