William, an employee for Williamson Corporation, receives an annual salary of $120,000 and is in the 28 percent marginal tax bracket. He is eligible to contribute to Williamson's 401(k) plan and could contribute the pretax amount of $12,000. Alternatively, he could contribute only $6,000 to the plan and use the remaining $6,000 to purchase municipal bonds paying 6 percent interest. Evaluate the tax savings and after-tax cash-flow effect of each of these investment choices. State which option you recommend for William and explain why.