The walkway is the diagonal of the square playground and divides the square into two right triangles making it the hypotenuse. If ss is the side length of the playground, then by Pythagorean Theorem, we can write:
[tex]\begin{gathered} s^2+s^2=18^2 \\ 2s^2=324 \\ s^2=162 \\ s=\sqrt[]{162} \\ s\approx12.7 \end{gathered}[/tex]A side of the playground is equal aproximately to 12.7 meters.