\(p_k(t) = \int \limits_{t}^\infty e ^{- r (s - t)} c(s) e^{-\delta (s - t)} ds\)
where the left-hand term is the price of capital goods, r is the discount rate, c is the cost of capital services, delta is depreciation and t is the time of acquisition of capital goods. If \(\dot p_k = 0\) in steady-state, differentiating with respect to t yields:
\(c = p_k ( r+ \delta)\)
which tells us that the cost of capital acquisition (or rental value of services) is the price times the forgone interest rate (of the sum of money) plus the rate of depreciation.  Thus, the desired level of capital will be:
    \(K^* = \alpha \frac{PY}{c}\)
In words, the desired capital stock is equal to the elasticity of output with respect to capital (how much revenues will change), times the price and quantity of output (revenue) over the price of capital.
Testable formula with parameter results:

Q-theory of Investment

"According to this approach, the principal way in which financial policies and events affect aggregate demand is by changing the valuations of physical assets relative to their replacement costs. Monetary policies can accomplish such changes, but other exogenous events can too... it is not to be expected that the essential impact of moentary policies and other ifnancial events will be easy to measure in the absence of direct observation of the relevant variables (q in the models). There is no reals to think that the impact will be captured in any single exogenous or intermediate variables..."