Question

Really need help I don't understand ​

Answer 1

we know the circumference shown for that picture is π miles, what would it be for the diameter?  namely how long is the diameter of that circle whose circumference is π miles?

$\bf \textit{circumference of a circle}\\\\ C=\pi d~~ \begin{cases} d=diameter\\ \cline{1-1} C=\pi \end{cases}\implies \pi =\pi d\implies \cfrac{~~\begin{matrix} \pi \\[-0.7em]\cline{1-1}\\[-5pt]\end{matrix}~~}{~~\begin{matrix} \pi \\[-0.7em]\cline{1-1}\\[-5pt]\end{matrix}~~}=d\implies 1=d$