A barrel of oil weighs 100 kilograms. After taking out 15 kilograms of oil, the oil weighs 81 kilograms more than the barrel. How much does the oil barrel weigh?
一桶油，连桶重100千克，取出15千克油后，这时油比桶重81千克，油桶重多少千克？
<gadget id="calculator">100 - 15 - 81</gadget>
<output>4</output>

<gadget id="calculator">4 / 2</gadget>
<output>2</output>

<result>2</result>