wait! i think i see. we haven't changed anything, have we?

ie we start with 75F - 201.5Fy
and to separate F, we just turn that into F (75 - 201.5y), which can be simplified (or whatever the term is) to 75F - 201.5Fy, but we don't want it written like that because we want to isolate F. am i on the right track?