Here's how to order 12 liters, 9 quarts, and 3 gallons from least to greatest:

1. Convert Everything to the Same Unit

Let's convert everything to liters, since that's the most straightforward conversion:

* 3 gallons: 1 gallon is approximately 3.785 liters, so 3 gallons is 3 * 3.785 = 11.355 liters

* 9 quarts: 1 quart is approximately 0.946 liters, so 9 quarts is 9 * 0.946 = 8.514 liters

2. Order the Quantities

Now we have:

* 8.514 liters (9 quarts)

* 11.355 liters (3 gallons)

* 12 liters (12 liters)

3. Final Order

From least to greatest:

1. 9 quarts (8.514 liters)

2. 3 gallons (11.355 liters)

3. 12 liters (12 liters)