Please Help I have attached the question....Please Help I have attached the question

Question 2: Washington paper company has estimated the costs of debt and equity capital (with bankruptcy and agency costs) for various proportions of debt in its capital structure as follows. Determine the company's optimal capital structure. Tax rate 40% Deb ratio B/ (B+E) Pretax Cost Cost of After-tax Cost Cost of of debt Equity of debt Equity 0 -- 14.00% 0.1 7.00% 14.20% 0.2 7.20% 14.60% 0.3 7.60% 15.40% 0.4 8.20% 17.00% 0.5 9.00% 20.00% 0.6 10.00% 26.00% WACC