Katherine filed her 2015 federal individual income tax return on April 15, 2016. It showed Katherine owed a balance due of $8,500. Katherine included a check for $1,000 when she filed her federal individual tax return, but she will not pay the remaining balance due of $7,500 until September 20, 2016. Katherine has received a bill from the IRS for interest on the unpaid federal tax of $7,500 and she has received a letter saying she will owe a penalty. What is the amount of Katherine’s late payment penalty? Please explain your answer and show your calculations.