A car moving at $8\mathrm{.}5$ m$/$s crashes into a tree and stops in $0\mathrm{.}22$ s$.$ What would the final velocity be$,$ in meters per second, if the car with the $72\mathrm{.}5-$kg passenger had collided with $($and stuck to$)$ a car that has an equal mass and is traveling in the opposite direction and at the same speed?