Two cars are driving towad each other along a straight road. their separation distance is l - (r1 + r2)t, where l is their original separation distance and r1 and r2 are their speeds. will the cars meet? when? what if they are going in the same direction and not driving toward one another? will they meet then?

The problem specifies that they are driving /towards/ each other along a straight road. Assuming they both dont turn around or stop, we know they will meet eventually, since they are continually moving straight towards each other. If they are both driving at the same, constant speed, they will meet at about half the road.
If they are going in the same direction, assuming they are both driving at a constant speed, they will never meet. One car will be constantly on the other’s tail, but since one car is constantly moving away from the other, they will never meet unless the first car (moving away from the other) stops or slows down enough so the other one catches up, or the car “chasing” the other speeds up enough to crash into the other.