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.)