Calculating future value and Present Value I have been stuck on this one for hours ... not too great at math can someone help. Thanks.

Isaac borrowed $\$4000$ at $11.5\%$ compounded quarterly $5.5$ years ago. 

One year ago he made a payment of $\$1500$. What amount will extinguish the loan today?

I've tried a bunch of different approaches, none were right.

From what I understand we should calculate the FV for $4.5$ years when $PV=\$4000$ 
then subtract $\$1500$ from answer and calculate FV for one more year.

But still no luck..
It sounds like your idea is correct. The current value of loan should be given by: $4000(1+ \frac{.115}{4})^{4 \times 5.5} - 1500(1+ \frac{.115}{4})^{4 \times 1}$

If you aren't getting the right answer, it could be a problem with using the calculator. Some can be difficult to use, for example, if they don't let you see what you are typing.

You also don't need to turn it into a multi step problem by calculating the value at 4.5 years, subtracting 1500, and then calculating the interest for the final year after everything else. If you calculate the current value of everything at once, you can save yourself some work. It is fairly easy to see that both must be equivalent if you draw a time diagram of the payments.
$$ $4,000*1.115^{18} = $28,379.68.$$ Paid off $$ $1,500 $$ Left to repay: $$ $26,879.69 $$
waited a year: $$ $26,879.69*1.115^4 = $41,545.47.$$

Unless, you mean, 11.5% per annum, compounded quarterly, then the interest would be: $$1 + (0.115/4) $$ Rather than simply $1.115$.