How can i do this? - Puzzle

There's two bare buckets:

a nine gallon one along with a four gallon one.

Somehow, I have to make six gallon.

How can i do this?

Before you go for the answer please comment your answer below!

Answer:

Fill the 3 gallon bucket and then pour it into the 5 gallon bucket.
Fill the 3 gallon bucket again.
Pour water from the 3 gallon bucket into the 5 gallon bucket until it is completely full.
You now have exactly 1 gallon left in the 3 gallon bucket.
Empty the full 5 gallon bucket.
Now, pour the 1 gallon of water into the empty 5 gallon bucket.
Fill the 3 gallon bucket again.
Finally, pour those 3 gallons into the 5 gallon bucket which still has 1 gallon in it.
Now you have exactly 4 gallons in the 5 gallon bucket!