Relatively simple

You need to measure out exactly 4l of water but you only have a 5l and a 3l container. How do you do it?

U fill da 5l bottle. Pour it into da 3l bottle. Poor out da 3l bottle and pour da 2l left from da 5l bottle into da 3l bottle. Fill up da 5 l bottle. Pour as much of the water as u can from the 5l bottle into da 3l bottle so that u have 4l remaining in da 5l bottle

Sounds good. You can also fill the 3, poor it into the 5. Refil the 3 and poor 2l into the five leaving you with 1l in the 3. Empty the 5l, poor the 1l from the 3l bottle into te 5l, then add another 3l.