If $ A=\{x\;/\;x\in\:N, \: $ and $\:x$ is a multiple of $3$ $\leq100\}$ and $B=\{x/x\in\:N\:$ and $\:x$ is multiple of $5$ $\leq\:100\}$, then no. of elements in $(A\times\:B)\cap\:(B\times\:A)\:is$

Question

$\begin{array}{1 1} 36 \\ 33 \\ 20 \\ 6\end{array}$