K Owed $9,500 in Taxes for 2012, Paid as Follows

Multiple Choice

K owed $9,500 in taxes for 2012, paid as follows: estimated tax payments of $2,100 each quarter, $1,000 with her Form 4868 (request for automatic extension) in March, and the remaining $100 with her Form 1040 in July.K's 2011 total tax was $8,000.What interest or penalty does she owe?

A) Failure-to-pay penalty
B) Interest on balance due
C) Penalty on underpayment of estimated tax
D) None of the above