Question 466938
Let x = speed of car B.  If car B is to overtake car A in 4 hours, then car A must have been on the road for  4 + 1 = 5 hours.  Hence the distance traveled by car A should have been (5 hr)*(80 km/hr) = 400 km.

==> 4x = 400 ==> x = 100 km/hr, the speed of car B.