You are a software programmer for a financial services company. You have been assigned the task of implementing a system to calculate the final interest rate and the total interest of a loan based on several factors, such as the applicant's credit score, the amount of the loan and the duration of the loan. The goal is to provide accurate information about interest rates to customers to help them make informed financial decisions. The base interest rate (BASE_RATE) is 6% and is adjusted according to the following table: