Two cars are travelling east along a straight highway at the same speed. At an intersection, the highway branches and splits into two straight roads, one heading approximately north-east and one heading approximately south-east. The angle betwen the two roads is 60 degrees. The two cars leave the intersection at the same time, one travelling north-east at 100 km/h and the other travelling south-east at 80 km/h. How fast is the distance between the two cars changing 30 minutes after they leave the intersection.

Two cars are travelling east along a straight highway at the same speed. At an intersection, the highway branches and splits into two straight roads, one heading approximately north-east and one heading approximately south-east. The angle betwen the two roads is 60 degrees. The two cars leave the intersection at the same time, one travelling north-east at 100 km/h and the other travelling south-east at 80 km/h. How fast is the distance between the two cars changing 30 minutes after they leave the intersection.