Isabel, a calendar-year taxpayer, uses the cash method of accounting for her sole proprietorship. In late December she received a $36,000 bill from her accountant for consulting services related to her small business. Isabel can pay the $36,000 bill anytime befor January 30 of next year without penalty. Assume her marginal tax rate is 37 percent this year and next year, and that she can earn a after-tax rate of return of 10 percent on her investments. Required: a. What is the after-tax cost if Isabel pays the $36,000 bill in December? b. What is the after-tax cost if Isabel pays the $36,000 bill in January? Use Exhibit 3.1. Note: Round your answer to the nearest whole dollar amount. c. Based on requirements a and b, should Isabel pay the $36,000 bill in December or January?