$\triangle ECD$ is similar to $\triangle EBA$, so
$$\frac{AE}{DE} = \frac{AB}{DC} = \frac{3}{9}=\frac{1}{3}.$$
Since $AE+DE=AD=4$, we have $AE=1$ and $DE=3$. From here, subtracting the area of $\triangle CED$ from $\triangle ACD$ will give you the answer.
$\triangle ECD$ is similar to $\triangle EBA$, so $$\frac{AE}{DE} = \frac{AB}{DC} = \frac{3}{9}=\frac{1}{3}.$$ Since $AE+DE=AD=4$, we have $AE=1$ and $DE=3$. From here, subtracting the area of $\triangle CED$ from $\triangle ACD$ will give you the answer.