A camera with a focal length f of 6 cm is used to take the picture of a person who is 180 cm tall, standing at a distance 3 m in front of the camera. How big will the image of that person be on film? How far behind the lens (assumed to be very thin) must the film be placed? I tried using the thin-lens equation and the equation of magnification, but I can't seem to be getting the right answer. (1/d o)+(1/d i)=(1/f) m=-(d i)/(d o) Using the first equation, I plugged in the numbers for f and d o and solved for d i. I know that there is something special with the signs, but I tried them every way possible, and I still can't get the right answer.