As it was not mentioned, we assume that it is a simple interest rate (it would be different if it was compound interest rate)
So we have now:
-
initial deposit of $800 (p=800)
- annual rate of 10% (r=0.1)
- leaves the account untouched for 8 years (t=8)
Apply the formula in the chart attached:

So the interest is 640$
Add this to the original deposit (800$) to get the full amount of money (the balance) after 8 years
800+640=1440$
Done!!
I hope that helps!