Draw a picture then analyse the triangle.
A security camera in a neighborhhod carnival is mounted on a wall 9 feet above the floor inside a video gallery. What angle of depression should be used if the camera is to be directed to a spot 6 feet above the floor and 12 feet from the wall?
There's a point where the security camera is, nine units above some base reference point (that's like, some convenient point on your paper that you choose). Then twelve units sideways from there and six units up from that convenient reference point you got a point where the camera's got to be looking.
Are you at all familiar with cartesian co-ordinates? It may be easier for me to describe what you've got to do if I mention you have two points (0,9) and (12,6) and you want the angle of the slope of the line joining them together.