Step 1: Understanding the relation between areas and sides of similar triangles.
The ratio of the areas of two similar triangles is the square of the ratio of their corresponding sides.
\[
\text{Ratio of areas} = (\text{Ratio of sides})^2
\]
Step 2: Applying the given ratio of areas.
We are given the ratio of areas as \( 81:121 \). Therefore:
\[
\left(\frac{\text{side 1}}{\text{side 2}}\right)^2 = \frac{81}{121}
\]
Step 3: Taking the square root of both sides.
\[
\frac{\text{side 1}}{\text{side 2}} = \sqrt{\frac{81}{121}} = \frac{9}{11}
\]
Thus, the ratio of the sides is \( 9:11 \). The correct answer is (A).