Anna does not make quarterly estimated tax payments even though she has substantial amounts of income that are not subject to withholding. In the previous year, Anna's tax liability was $ 18,000 and her AGI was$ 135,000. In the current year, Anna's actual tax liability is $30,000, and $18,200 was ,vithheld from her salary.

a. Is Anna subject to the underpayment penalty? Why?

b. If Anna's withholdings were only $15,000, would she be subject to the underpayment penalty? Why?

c. If Anna is subject to an underpayment penalty, can she deduct this amount as interest? Explain.