Your question is Measure Exactly Four Gallons. Take a moment with it on the right.
Talk me through your thinking if you like. When you're confident, submit your answer and I'll grade it like a real screen (7/10 or better passes).
You have two buckets. One holds exactly five gallons and the other three gallons. How can you measure exactly four gallons of water into the five gallon bucket? Assume you have an unlimited supply of water and that there are no measurement markings of any kind on the buckets.