Elki would like to invest $50,000 in tax­exempt securities. He now has the money invested in a certificate of deposit that pays 5.75 percent annually. What rate of interest would the tax­exempt security have to pay to result in a greater return on Elki’s investment than the certificate of deposit? Work the problem assuming that Elki’s marginal tax rate is 12 percent, 22 percent, 24 percent, and 32 percent.