We replace in the formula:
[tex]A=P(1+\frac{r}{n})^{nt}[/tex]Where P is the initial balance, r is the interest rate, n is the number of times interest is applied per time period and t is the number of time periods. We replace as follows:
[tex]A=(200)(1+\frac{0.12}{12})^{(12)(9)}[/tex][tex]\Rightarrow A=585.78515851\Rightarrow A\approx585.79[/tex]So, Darnel will earn approximately $585.79.