DETERMINATION OF INTEREST RATES. You decided to go and apply for a credit card at your local financial institution. The Prime rate currently announced was $6\mathrm{.}25\%.$ You have an excellent credit history and FICO score of $800.$ You were offered $21\mathrm{.}99\%$ interest rate for a rewards card that has cash back. How is each interest rate, which you and other borrowers receive from a lender or credit company, determined or calculated by the creditors or institution?