4. Assume corporate tax rates of 15 percent on the first $50,000 of taxable income, 25 percent on taxable income between $50,000 and $75,000, 34 percent on taxable income between $75,000 and $100,000, and 39 percent on taxable income between $100,000 and $335,000. If a corporation estimates its pretax income at $20,000 for the first quarter, $25,000 for the second quarter, $30,000 for the third quarter, and $35,000 for the fourth quarter, its estimated annual effective tax rate is:

a 23.77 percent b 25 percent c 24.67 percent d 34 percent