Answer:
Andy went as furthest as possible with a gallon of gasoline
Explanation:
Let 
 
m ----> the distance in miles 
 
g ----> the number of gallons of gas 
 
step 1 
 
Kelley's Mileage 
 
Find the slope of the linear function of Kelley's Mileage 
 
we have the points 
 
(0,0) and (20,50) 
 
 
 
the linear equation is 
 
 
 
step 2 
 
Andy's Mileage 
 
Find the slope of the linear function of Andy's Mileage 
 
we have the points 
 
(15,78.75) and (30,157.5) 
 
 
 
the linear equation is 
 
 
 
step 3 
 
Rick's Mileage 
 
we have 
 
 
 
therefore 
 
the slope is 
 
step 4 
 
Compare the slopes 
 
 
 
therefore 
 
Andy went as furthest as possible with a gallon of gasoline