AHSME 1961 Problem 2

An automobile travels $a/6$ feet in $r$ seconds. If this rate is maintained for $3$ minutes, how many yards does it travel in $3$ minutes? $\textbf{(A)}\ \frac{a}{1080r} \textbf{(B)}\ \frac{30r}{a} \textbf{(C)}\ \frac{30a}{r} \textbf{(D)}\ \frac{10r}{a} \textbf{(E)}\ \frac{10a}{r}$