At that time, what did it cost to buy
gallons of gas?
Multiply the cost by the number of gallons to determine what the cost would be.
for a tank of gas. How many gallons did he buy?
This is the opposite of part (a). You know what the cost is, so divide the final price by the cost per gallon.
At right is a graph of this situation. Predict how the line would change to represent the average cost of gas in December of 2005, when gas cost
per gallon on average.
The line would get steeper.