18 inches
Explanation
the area of a square is given by:
[tex]\begin{gathered} \text{Area}_{square}=side\cdot side \\ \text{Area}_{square}=side^2 \end{gathered}[/tex]then ,let
[tex]\text{Area}=A=324in^2[/tex]replace
[tex]\begin{gathered} 324in^2=side^2 \\ \text{square root in both sides} \\ \sqrt[]{324in^2}\text{ = }\sqrt[]{side^2} \\ 18\text{ in=side} \end{gathered}[/tex]therefor, the length of the side is 18 inches.
i hope this helps you