Answer:
$4.50
Explanation:
To solve a problem like this one, we can use the simple ratio method to find the cost for 9 liters, here in this case.
We know that, 5 liters (of something) cost $2.50. So to find the cost for 9 liters, we can assume its cost to be x and can write it as:

Now solving for x to get:


Therefore, 9 liters would cost $4.50.