Assume that a hospital makes $150 purchase on the first day of the month and must pay a $5 late fee if it doesn't pay within the first 15 days. What is the annual interest rate if the hospital pays on day 16? Day 30? I know that the correct answers are: Annual interest rate on day 16: 1216.67% Annual interest rate on day 30: 81.1% However, I am unsure to arrive at those answers. Please help!