Step 2 of 8: Sketch the Optical System

Don't use a computer for this step. Use a piece of paper.

Just do it. I know that you're clever and can keep everything in your head at once (especially for this trivial system). Your sketch should have an optical axis and all the optical elements. In this case that means an object plane, the lens, and the image plane.

System Sketch

If you don't have a sketch, then you won't be able to play along at home.