(I don't know if this is the method you are supposed to use, but I believe you will still get the same answer!)
Answer: 20 g butter, 10 g sugar, 30 g flour
Explanation: First off, if we look at 3 and 18, you notice that three is a factor or 18, going into the number 6 times.
So, if you are making 6 times less of the original amount, divide each measurement by six to give you your answer.
120/6 = 20
60/6 = 10
180/6 = 30