Bill files as head of household in 2015. He had taxable income of $90,000, including the sale of stock he held for investment for two years for a $20,000 gain. Bill sold no other assets during the year, and he did not have any capital loss carryovers.

a. What is Bills 2015 tax liability?

b. What would Bills 2015 tax liability be if he had held the stock for 10 months?