why does B/(S+B)= 3/7 and S/(S+B)= 4/7?

Calgary Industries, Inc., is considering a new project that costs $25 million. The project will generate after-tax (year-end) cash flows of $7 million for five years. The firm has a debt-to-equity ratio of 0.75. The cost of equity is 15 percent and the cost of debt is 9 percent. The corporate tax rate is 35 percent. It appears that the project has the same risk of the overall firm. Should Calgary take on the project? B/S=0.75 B/(S+B) = 3/7 S/(S+B) = 4/7 WACC = [(4/7) x 15%] + [(3/7) x 9% x (1-0.35)] = 11.08% NPV =-$25 million+ $7 million = $819,299.04 Undertake the project t=1 (1+0.1108)