Answer:
It is more convenient to fill up in the United States.
Step-by-step explanation:
We convert a US gallon to liters:
1 Gallon equals 3.78541 liters.
Therefore, 1 US Gallon costs (3.78541) x (1.29) = 4.8831789 Canadian dollars.
Now we convert the price of a US gallon in Canadian territory to US dollars:
4.8831789 * 0.79 = 3.85771133 US dollars.
Conclusion: A gallon purchased in the United States costs 2.58 US dollars, while a gallon in Canada is equivalent to 3.85771133 US dollars. This way it is more convenient to fill up in the United States.