A barrel of oil, after 6 kg is used, the remaining 6 kg is more than what was used. How many kg is the barrel of oil originally?
一桶油，用去6千克后，剩下的比用去的还多6千克，这桶油原来有多少千克？
<gadget id="calculator">6 + 6 + 6</gadget>
<output>18</output>

<result>18</result>