First National Bank has a debt$-$to$-$equity ratio of $3.$ Its weighted average cost of capital

is $12\mathrm{.}50\%$ and its cost of debt is $8\%.$ First National Bank is subject to a $25\%$ corporate

tax rate.

a$.$ What is First National Bank cost of equity?

b$.$ What is First National Bank un$-$levered cost of capital?

c$.$ What would be its weighted average cost of capital is debt equity ratio is $0\mathrm{.}5?4?$