A company$$s capital structure consists of $25\%$ debt and $75\%$ common equity. The company has a $20\%$ tax rate, and the cost of equity is $14\%.$

What is this company$$s difference in weighted average cost of capital $($WACC$)$ if the cost of debt is $6\%$ at market value and $5\%$ at book value and the cost of equity is $12\%?$

a$.0\mathrm{.}19\%$

b$.0\mathrm{.}25\%($b is correct, I just don't understand how.$)$

c$.10\%$

d$.11\%$