Answer:
The overall trip takes 30 hours.
Explanation:
Let the time taken on one trip = x ( in hours)
It is given that the time taken on the return trip = (30-x) hours.
As, the average speed for both side of the trips is 70 mph and 28 mph respectively.
Also, as

So,

As for both sides of the trip distance will remain same.
We get,

i.e.

i.e.

i.e.

i.e. x= 8.6 hours
So, the time taken for the forward trip is 8.6 hours
Then, the time taken on the return trip is (30-x) = (30-8.6) = 21.4 hours.
Thus, the total number of hours for the round trip = 8.6 + 21.4 = 30 hours.
Hence, the overall trip takes 30 hours.