Answer:
4.02 gallons
Explanation:
From the illustration:
$0.750 USD = $1.00 CAD
Therefore,
$20 USD = 20 x 1/0.750 = $26.667 CAD
The cost of gas in the US is 2.21 USD per gallon.
20 USD will be able to get 20/2.21 = 9.05 gallons
The cost of gas across the border is 1.40 CAD per liter.
0.264 gallon = 1 liter
1 gallon = 1/0.264 = 3.788 liters
This means that 1 gallon = 3.788 x 1.40 = 5.303 CAD
Hence, 26.667 CAD will get 26.667/5.303 = 5.03 gallons
If he buys a $20 USD gas before crossing the border, Carl will get 9.05 gallons, but if he buys it after crossing the border, he will get 5.03 gallons. Therefore, if he buys the gas before crossing the border instead of buying it in Canada, he will get 9.05 - 5.03 = 4.02 gallons extra.