Let \( a, ar, ar^{2},\ldots \) be an infinite G.P. If \( \sum\limits_{n=0}^{\infty}ar^{n}=57 \) and \( \sum\limits_{n=0}^{\infty}a^{3}r^{3n}=9747 \), then \( a+18r \) is equal to
\( 38 \)
\( 46 \)
\( 27 \)
\( 31 \)