For similar triangles, the ratio of their areas is the square of the ratio of their sides.
\[
\left(\frac{\text{Perimeter}_1}{\text{Perimeter}_2}\right)^2 = \frac{\text{Area}_1}{\text{Area}_2}.
\]
\[
\left(\frac{P_1}{P_2}\right)^2 = \frac{9}{4}.
\]
\[
\frac{P_1}{P_2} = \frac{3}{2}.
\]
Thus, the ratio of their perimeters is \( 3:2 \).