Question 873419
You are correct. Assuming it's compounded annually, you plug in


P = 800 (the amount loaned)
r = 0.15 (15% = 15/100 = 0.15)
n = 1 (compounding 1 time per year)
t = 4 (number of years)


If you are compounding at different rates, then you change the value of n. For example, if you compound it quarterly, then you compound 4 times a year (so n = 4). If you compound monthly, then n = 12.