Hi-Tech, Inc. has determined that it can minimize its weighted average cost of capital (WACC) by using a debt-equity ratio of 2/3. If the firm's cost of debt is 9% before taxes, the cost of equity is estimated to be 12% before taxes, and the tax rate is 40%, what is the firm's WACC? Note that only 1pt is eligible for the correct answers without showing the calculation work.

A) 6.48%

B) 7.92%

C) 9.36%

D) 10.80%