Jana Novotna of what is now the Czech Republic has the strongest serve among her fellow tennis players. In $1993,$ she sent the ball flying with a speed of $185$ km$/$h$.$ Suppose a tennis ball moving to the right at this speed hits a moveable target of unknown mass. After the one$-$dimensional, perfectly elastic collision, the tennis ball bounces to the left with a speed of $80\mathrm{.}0$ km$/$h$.$ If the tennis ball's mass is $5\mathrm{.}70$ x $10-2$ kg$,$ what is the target's mass? $($Hunt: Use the conservation of kinetic energy to solve for the second unknown quantity.$)$