Serial Music has a long standing policy of financing with $50\%$ debt, $50\%$ equity at book values. The average interest rate on existing debts is $4\mathrm{.}5\%,$ but new debt can be issued at $3\mathrm{.}5\%.$ Its common stock is trading at two times book value per share. The cost of equity is $9\mathrm{.}5\%.$ The corporate tax rate is $21\%.$ What is Serial's after tax WACC?