Given:
Interest rate = 3.9% compounded monthly.
The annual percentage yield is calculated as,
[tex]\begin{gathered} \text{APY}=(1+\frac{r}{n})^n-1 \\ \text{APY}=(1+\frac{3.9}{100\times12})^{12}-1 \\ \text{APY}=(1.003325)^{12}-1 \\ \text{APY}=0.0397 \\ \text{APY}=3.97\text{ \%} \end{gathered}[/tex]Answer: annual percentage yield is 3.97 %