In a survey using a double-sampling (two-phase) design to estimate a population mean $\bar{Y}$, the cost function is $C = c_0 + c_1n' + c_2n$. If the variance of the estimator is $V = \frac{W_2^2 S_{2y}^2}{n} + \frac{S_1^2}{n'} - \frac{S_1^2}{N}$, which relationship represents the optimal allocation to minimize cost for a fixed variance?