$7\mathrm{.}1-7.$Two asteroids collide head$-$on and stick together. Before the collision, asteroid A $($mass $1,000$ kg$)$ moved at $100$ m$/$s$,$ and asteroid B $($mass $2,000$ kg$)$ moved at $80$ m$/$s in the opposite direction.

Use momentum conservation $($make a complete Momentum Chart$)$ to find the velocity of the asteroids after the collision.