A certain country uses a progressive tax system. The amount of tax consists of a linear part proportional to the income and a nonlinear part depending on the income by a power law. The total amount of tax is determined by the formula

T(W) = 0.59W + (0.82W + 930)^2.77

where W is the income; and 2.77 is the exponent. At what level of income the tax rate will be minimal?