We have that the area of the infield is 81 in2.
This area is a square, which means it has equal sides, and its area is:
[tex]\text{Area}=side^2[/tex]
If the area of the square is 81 in2, we have that:
[tex]\begin{gathered} \text{side}^2=81 \\ \text{side}=\sqrt{81} \\ \text{side}=9\text{ in} \end{gathered}[/tex]
So the side of the infield is 9 inches.
