Can Someone please explain what i'm looking for?

[kpangrace]

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? that's 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!?

 

[Doc Al]

... am i just looking for the length of all of the red line?

That's it. That's the distance the light travels from object to camera. You'll have to use your knowledge of the laws of reflection to find that distance.