To find the answer, we will have to find the percentage of $273 to $ 3500, and we can use the formula:
[tex] \frac{interest received}{investment amount} \times 100% [/tex]
In this case:
273/3500 x 100%
=39/500 x 100%
=7.8%
Therefore the annual interest rate would be 7.8%.
Hope it helps!