In 2018, Juanita is married and files a joint tax return with her husband. What is her tentative minimum tax in each of the following alternative circumstances?
a. Her AMT base is $100,000, all ordinary income.
b. Her AMT base is $250,000, all ordinary income.
c. Her AMT base is $100,000, which includes $10,000 of qualified dividends.
d. Her AMT base is $250,000, which includes $10,000 of qualified dividends.