Answer:
B. 16 hrs
Explanation:
Distance = rate × time
The best way to do this is to make a table with the info. We are concerned with the trip There and the Return trip. Set it up accordingly:
d = r × t
There
Return
The train made a trip from A to B and then back to A again, so the distances are both the same. We don't know what the distance is, but it doesn't matter. Just go with it for now. It'll be important later.
d = r × t
There d
Return d
We are also told the rates. There is 70 km/hr and return is 80 km/hr
d = r × t
There d = 70
Return d = 80
All that's left is the time column now. We don't know how long it took to get there or back, but if it took 2 hours longer to get There than on the Return, the Return trip took t and the There trip took t + 2:
d = r × t
There d = 70 × t+2
Return d = 80 × t
The distances, remember, are the same for both trips, so that means that by the transitive property of equality, their equations can be set equal to each other:
70(t + 2) = 80t
70t + 140 = 80t
140 = 10t
14 = t
That t represents the Return trip's time. Add 2 hours to it since the There trip's time is t+2. So 14 + 2 = 16.
B. 16 hours