This is the second time i am posting this question. The solution is "bearing Set B", I just want to learn how to work my way to that answer. The previous Expert got it wrong, PLEASE take your time and answer thoroughly.

Three types of bearing sets (A,B,C) could replace worn-out bearings. Set A will cost $7.50 and last 4 years, Set B will cost $8.00 and last 6 years, and Set C will cost $30.00 and last 12 years. Which bearing would you choose if interest rate is 5% per year