Answer :
i think you can weigh it 3 and 3.
If they balance, choose set not used.
If not balanced, take the heavier side
then weigh 1 and 1
if balanced, stone not used, if not balanced, take the heavier side
hope this helps
If they balance, choose set not used.
If not balanced, take the heavier side
then weigh 1 and 1
if balanced, stone not used, if not balanced, take the heavier side
hope this helps