West Corporation has $50,000 which it plans to invest in marketable securities. The corporation is choosing between the following three equally risky securities: Alachua County tax-free municipal bonds yielding 6 percent; Exxon bonds yielding 9.5 percent; GM preferred stock with a dividend yield of 9 percent. West's corporate tax rate is 35 percent. What is the after-tax return on the best investment alternative? (Assume the company chooses on the basis of after-tax returns.) a. 8.06% b. 7.13% c. 6.18% d. 6.55% e. 6.00%