Answer:
The distance between two cities is 60 miles.
Explanation:
Time taken to travel from B to A = 2 hours
Time taken to travel from A to B = 1.5 hours
Current speed = 5 mph
Let the speed of ferry in still water = u mph
When the ferry moves with the current, it will taken lesser time (i.e. A to B) and when it moves against the current it will take more time (i.e. B to A).
Let the distance between the two cities A and B = D miles
While moving with the current, speed =

While moving against the current, speed =

Formula for Distance = Speed
Time
Distance traveled in each case is same i.e. D.
So,

Now,

So, the distance between two cities is 60 miles.