Let s = Car B's speed
Car B is 15 mph faster than A, therefore
(s - 15) = Car A's speed
Write a distance equation; dist = speed * time
2(s-15) = 1.5s
2s - 30 = 1.5s
2s - 1.5s = 30
.5s = 30
s = 60 mph is car B's speed
Confirm this find the distances, they should be equal
2 (60-15) = 90
1.5 (60) = 90