Answer:
To find out how many miles per gallon the truck got, we can divide the number of miles it traveled by the number of gallons of gas it used: 84 miles / 4 gallons = <<84/4=21>>21 miles/gallon.
To find out how many miles per gallon the SUV got, we can divide the number of miles it traveled by the number of gallons of gas it used: 72 miles / 3 gallons = <<72/3=24>>24 miles/gallon.
To find out how many more miles per gallon the SUV got than the truck, we can subtract the number of miles per gallon the truck got from the number of miles per gallon the SUV got: 24 miles/gallon - 21 miles/gallon = <<24-21=3>>3 miles/gallon.
The SUV got 3 more miles per gallon than the truck.
Explanation: