Express X in Y

>I made the formula as compact as possible
it may be clearer if you show the original problem

>>350440
It's a macro-economic investment function. It's based on the idea that the production in an economy is given by a Cobb-Douglass production function, which is:
y=(A*L)^0.5 * (C/k)^.5
where y is the total output of the ecoomy,
A = disembodied labour productivity
L = people employed
C = capital
k = output to capital ratio

>>350446
New investments are based on the marginal utility of a piece of investment, the weighted average cost of capital (wacc), utilization of capacity, the depreciation and the time expected to earn back the investment

>>350447
The big idea is to calculate the marginal utility of additional capital and divide it by the cost of that capital. This yields a certain ROI.

However, I want the formula to have a ROI as input, and the capital as output.

omg i see 9+1 omg i am crying....