I’m fairly sure that’s more reciting a solution learned from memory than doing math. What does it answer to

“How do I measure 12 liters when I have a 15 liter bottle and a 9 liter bottle?”

or

“How do I measure a liter when I have a 750 ml milk carton and a 12½ dl tea pot?”

I think we expect an AGI to be able to answer them, even though quite a few intelligent humans wouldn’t be able to do that.

OTOH, ChatGPT also agrees with kurisufag.

I entered your prompt and got the same reply from ChatGPT. Then I changed "4 liters" to "4 gallons" and got this:

  To measure 4 gallons of liquid using a 3-liter and a 5-liter bottle, you would need to convert gallons to liters first. One gallon is approximately equal to 3.785 liters, so 4 gallons is approximately equal to 15.14 liters.
   
  Since the available bottles have capacities of 3 liters and 5 liters, you will need to fill and empty the bottles several times to reach the target of 15.14 liters. Here's one way to do it:
  
    Fill the 5-liter bottle with water.
    Pour the water from the 5-liter bottle into the 3-liter bottle until it's full, leaving 2 liters of water in the 5-liter bottle.
    Pour the 2 liters of water from the 3-liter bottle into a separate container.
    Repeat steps 1-3 two more times, which will leave you with a total of 6 liters of water in the separate container.
    Fill the 5-liter bottle with water again and pour as much as possible into the separate container until it's full. This will add 3 liters of water to the container, for a total of 9 liters.
    Fill the 3-liter bottle with water and pour it into the separate container until it's full. This will add another 3 liters of water to the container, for a total of 12 liters.
    Fill the 3-liter bottle with water again and pour as much as possible into the separate container until it's full. This will add 1 liter of water to the container, for a total of 13 liters.
    Fill the 5-liter bottle with water and pour as much as possible into the separate container until it's full. This will add another 2 liters of water to the container, for a total of 15 liters, which is approximately 4 gallons.
  
  Keep in mind that this method is approximate and assumes that 1 gallon is equal to 3.785 liters. If you need a more precise measurement, you may need to use a measuring container that is calibrated in gallons.

Starts off OK. Notice that it's eventual goal is to get 15 liters: good! But then it doesn't understand what it's doing so it messes around with the 3 liter bottle instead of knowing 3*5=15. Additionally, one of the times it fills the 3 liter bottle and pours all of it out but somehow only produces 1 liter.

And it uses the 5 liter bottle to top up the separate container leaving 2 liters, and then proceeds to fill up the separate container.

Looks like it's mixing up elements of the solution to the original problem without understanding how the topping up works, with the solution to a different problem that it felt was sufficiently related. It's a wild guess based on similarity.