Substitute Circular referencing with algebra equation

Hi everyone,

I am having a bit of issues with some estimates.
Whilst trying to calculate some costs I came up with a circular reference (Projects cost, interest on loan and total cost...

I have attached an example Spreadsheet of what it is that I am trying to get to and hopefully one of you keen-eyed people can spot my mistake?
Essentially it is taking the original cost, finding out a percentage cost of the interest (based on whole project), which is considered to be a cost of the whole, and then I output the total cost of the project. The solution I am trying to get to is along the line of 0,03y + 12345 (all known fix costs) = y. Solving for Y gives then the answer 0,97, which I then divide with the total known costs, thus giving me an end value for the projects total costs.

I hope this made sense or that the file is set up sensibly... if not please do ask questions!

Many many thanks for you help guys!
Kurifodo

CR_Example.xlsx

An updated version of the file where the problem is a bit clearer... I hope!

Hi... any tips on the issue?

Still trying to work it out and I only seem to go round in circles and genuinely can't see where my logic is failing

Thanks guys!

It seems to work great! I have some other CR's that need addressing before I can say for sure, but so far so good!
Would you mind explaining the logic behind your change to SUM(G$17:G$18)? I don't quite see why it works! :O

Thanks a lot !!