You are trying to photograph a bird sitting on a tree branch, but a tall hedge is blocking your view. However, as the drawing shows, a plane mirror reflects light from the bird into your camera. If x = 3.1 m and y = 4.0 m in the drawing, for what distance must you set the focus of the camera lens in order to snap a sharp picture of the bird's image? Ok so all i need to find out is what exactly do they mean about setting the focus to get the sharpest picture...... am i just looking for the length of all of the red line? thats what i'm assuming but i want to be sure.... or is it just part of the red line??? anyone want to answer this simple question for me!?