Q: Calculate the total present value of the following payments:

$600 made at the end of each of the years 1 to 8

$900 made at the end of each of the years 9 to 15

if the annual effective interest rate is 7.5% for the first ten years and 9% thereafter.

I tried to use the present value formula:

PV = X(1+i)^-t

but dun know if it's right or wrong, and does the question have anything to do with the force of interest?

Please help, thanks alot!!!