Yes I can see we can derive that the fuel tank cg station is near station 38.
However, and this puzzles me a bit, I have 3 manuals here for the C152, C172 and C182, and I see no reference to the fuel tanks cg arm. Cessna states that you don't need to use the cg arm on the "loading problem", you just use the graph, which of course works fine.
But I really think somewhere we should have the arm for the fuel tanks. And where exactly did the author of those W&B spreadsheets find that constant value to multiply the weight?
Different constants for different positions. I'm just curious about that.
I realized this missing fuel tank arm issue the other day, when I tried to calculate the CG without using the graph. I had no information for the fuel tank arm. So I went to the spreadsheet and found the constant, which is even more mysterious to me at this point.