A $3\mathrm{.}0-$kg and a $5\mathrm{.}0-$kg box rest side$-$by$-$side on a perfectly smooth, level floor. A horizontal force of $32$ N is applied to the $3\mathrm{.}0-$kg box pushing it against the $5\mathrm{.}0-$kg box, and, as a result, both boxes slide along the floor. How hard do the two boxes push against each other?

$24$ N$20$ N$32$ N$12$ N$0$ N