a) Keith's car will have less gas.
Locate the point in which miles driven = 90 (Between 60 and 120)
Since Keith's line is lower than Carmen, he has less gas.
We can also find the difference: 11 - 10 = 1.
It will have 1 less gallon.
b) Look at the point in which both lines meet. This means that they have the same amount of gallons remaining (8) at 180 miles driven.
Before 180 miles, Keith's car will always have less car remaining.