This problem simulate an arithmetic series:
End of First year -- 500
End of Second year -- 500 +25
End of Third year -- 500 +50
...
500, 525, 550, ...
\(a_{16} = 500+25(15)\)
\(a_{16} = 875\)
\(s_{16} = \frac{16}{2} (500+875)\)
\(s_{16} = 11~000\)
The accumulated value of the investment after 16 years is 11, 000 dollars