Answer:
To travel 68 miles, Changs need 4.53 gallons of gas.
Solution:
From question it is given that the Changs traveled 375 miles on 25 gallons of gas.
We need to find out many gallons of gas do they need to travel 68 miles
To find out how many gallons of gas is needed to travel 1 mile we do the following:

So 0.066 gallons of gas is required to travel 1 mile.
Therefore to travel 68 miles the amount of gas we need is

So, 4.533 gallons of gas is required to travel 68 miles by the Changs