4.If you pay the minimum payment per month of $40.28 on your credit card, you will pay it off after making 97 payments. If you pay $10 more per month, you will pay it off 33 months sooner. How much total interest will you save?

5.Your best friend opened an investment account with a deposit of $196.76 today. They will continue to deposits every two weeks into an account that they hope will earn an interest rate of 8.06% per year. How much will they have in 13 years?

6.An investment will give you monthly payments of $625.8 for 11 years. You will receive your first payment today. If your required return is 9.6%, what is it worth today?

Please answer with formulas. thanks