Answer:

Explanation:
Let
g ----> number of gallons of gasoline
c ---> the total cost in dollars
we have
First gas station

This is a proportional relationship between the variables c and g
The constant of proportionality k or unit rate (slope) is equal to

Second gas station
we have the ordered pairs
(2.5,8.30) and (5,16.60)
This is a proportional relationship between the variables c and g
The constant of proportionality k is equal to

the linear equation is

To find out how much per gallon would Billy save, subtract the unit rate of the Gas station 1 from the unit rate of the Gas station 2
so
