Donna files as a head of household in 2016 and has a taxable income of $90,000, including the sale of a stock held as an investment for two years at a gain of $20,000. Only one asset was sold during the year and Donne does not have an capital loss carryovers.

a. What is the amount of Donna's tax liability?

b. What is the amount of Donna's tax liability if the stock is held for 11 months?