You just bought expensive car stereo for $2,400 online at Mississippi Best store. The store offered you a choice X% discount if you pay right now or you can pay within six months. You can borrow money at your bank at 8.40% per annum compounded monthly.

What is the lowest X% for which you will pay the store right now?

You should answer as the percentage. For example if the answer is 14.5%, then enter 14.5 as the answer.

(Hint: Refer to the Cash Discount Practice Problem. Assume 360 days in a year. Monthly bank interest rate to be paid is annual rate/12)