Firsts of this is not my problem I don't even take physics but it is my girlfriends. She doesn't know how to get the answer an neither do I. I took some physics but not enough for this. 1. The problem statement, all variables and given/known data A sports photographer has a 160-mm-focal-length lens on his camera. The photographer wants to photograph a sprinter running straight away from him at 5.5 m/s . QUESTION: What is the speed (in mm/s) of the sprinter's image at the instant the sprinter is 12 m in front of the lens? 2. Relevant equations 3. The attempt at a solution I did some research online and through the book and I understand what it is asking. I visualize the problem in my head but I can't find the correct equations for this. We just need some guidance on where to look or what equations to use and maybe how to use them. Thank you physics forums community.