Need help building an autonomy formula, able to self-arrange itself

Question

Hi again, folks! I've recently been helped by Barry in some of my problems with Numbers and formulas, and he helped me a lot, but I need a new help. Please, notice that I have no idea about spreadsheets, mathematics and such, but a creative mind As well, English is my second languaje, so expect some errors in my grammar and the like
I'm now needing some numbers to re-arrenge by themselves taking some criterias as reference. I don't know what I have to do, I just know the basic formulas and a very basic knowledge of 'if statements', so I'm naked on this.
So... I have 3 cells, for example, A, B and C.
· Cell A has an amount.
· Cell B has an amount which is handled by Cell A through a formula in Cell B.
· Cell C displays the total amount from Cell B (and other cells, but I think that doesn't matter right now), so values in Cell C dependes on a formula which sums   from other cells.
So, the criteria is this:
1. If value in Cell C is under 200, Cell B should increase its value till Cell C reaches amount = 200.
2. If value in Cell C is above 200, Cell B should decrease its value till Cell C reaches amount = 200.
3. Amount in Cell A should remain unaffected by these changes.
The problems are: amount in Cell B is determined by the amount in Cell A plus a formula in Cell B.
This is:
1. Cell A has a number, for example, 20.
2. Cell B has a formula which states that any value in Cell A must be multiplied by 2 and summed by 40 (=2*B4+40) without parentesis. The reason of this is because each increaement in Cell A should apply 2 increments in Cell B. So for example:
Cell A = 20.
Cell B = 50.
If I increase A to 21; B is 52; if A=22; B=54; etc.
Now the problem is that the number in Cell B increases a final amount in Cell C. And here is the main problem. Amount in Cell C must not go beyond 200. So the criteria is what I wrote above, in So, the criteria is this: "..."
So well... I'm literally stuck there because I cannot make this work so if anybody knows, I'm all eyes.
Ø3

Answer 1

The problem you will find is that this is a circular reference.  The value of C depends on the value of B while, at the same time, the value of B depends on the value of C.  So you cannot do it the way you are thinking.
If I understand what you said,
A = an amount you enter by hand
B = 2*A+10 + whatever it takes to get C to be exactly 200.
C = B + some other cells.  I'll use C=B+D.
So, the result will be:
A = an amount you enter by hand
C = 200 , also entered by hand. You want it to always be 200 so put that number in the cell.
B = C-D
However, this totally negates your original purpose of having B=2*A+10 (this formula is based on your example numbers for A and B). The value in A has no affect whatsoever on the value in B or C.