A $29\mathrm{.}5-$g object moving to the right at $21\mathrm{.}0$ cm$/$s overtakes and collides elastically with a $13\mathrm{.}0-$g object moving in the same direction at $15\mathrm{.}0$ cm$/$s$.$ Find the velocity of each object after the collision. $($Take the positive direction to be to the right. Indicate the direction with the sign of your answer.$)$