Determine the taxable amount of social security benefits for the following situations.

a. Erwin and Eleanor are married and file a joint tax return. They have adjusted gross income of $39,600, no tax-exempt interest, and $13,860 of Social Security benefits. As a result, $______ of the Social Security benefits are taxable.

b. Assume Erwin and Eleanor have adjusted gross income of $16,200, no tax-exempt interest, and $17,820 of Social Security benefits. As a result, $______ of the Social Security benefits are taxable.

c. Assume Erwin and Eleanor have adjusted gross income of $116,000, no tax-exempt interest, and $17,400 of Social Security benefits. As a result, $_______ of the Social Security benefits are taxable.