The capital structure for McKesson is provided below. If the firm has a $3\mathrm{.}5\%$ after tax cost of debt, $6\%$ commercial loan rate, a $13\mathrm{.}5\%$ cost of preferred stock, and an $18\%$ cost of common stock, what is the firm's weighted average cost of capital $($WACC$)?[$a$]$

Note: format is ${?}^{}.\%$

Capital Structure $($in $K^{\text{'}}s)$

Bonds

$$,1,083$

Commercial Loans

$ $,2,845$

Preferred Stock

$$268$

Common Stock

$$,3,681$