Answer:
3
Explanation:
This is basically finding the rate of the truck and the rate of SUV.
Rate of truck: 84 divided by 4=21
The rate of the truck is that it can travel 21miles per gallon.
Rate of SUV: 72 divided by 3=24
The rate of the SUV is that it can travel 24miles per gallon.
How many more miles did the SUV travel per gallon than the truck is 24-21=3miles.