[tex]\bf \stackrel{\stackrel{\textit{distance around it\qquad \qquad }}{\downarrow \qquad\qquad }}{\textit{circumference of a circle}}\\\\ C=\pi d~~ \begin{cases} d=diameter\\[-0.5em] \hrulefill\\ C=56.55 \end{cases}\implies 56.55=\pi d\implies \cfrac{56.55}{\pi }=d\implies 18\approx d[/tex]
