I used to love ray tracing
the big secret is: you do a diagram, and any ray parallel to the x axis is bounced thro the focal point - that is the brown line
as for your second part
none of us better answer - there are two conventions RIP NCCC ( real-is-positive ) or ( New cartesian coordinate convention) and they give opposite answers ( neg means imaginary image OR distance from observer)
pay more attention to your lessons rather than asking us who did it 50 y ago !
( and we all probably did it in cms as the metric system was then CGS and jjust changing ( to MKS then rationalised MKS and then SI )