If a person does not pay taxes before the due date, an interest is charged on the amount that has to be paid till the date it is actually paid.
The rate of interest is not a constant one and is calculated again after a period of every three months. It is equal to the 3% more than the federal short term rate prevailing then.
For March 2010, the rate is 4%.
This interest is compounded on a daily basis which would make the actual interest payment very high effectively. Also, there could be various other charges levied for not paying the taxes in a prompt manner. The correct answer is 4% or option D.