A barrel of oil weighs 100kg, and a barrel of oil weighs 80kg. How many kilograms of oil are taken from barrel A and put into barrel B so that the mass ratio of oil in barrels A and B is 7:11?
甲桶油重100kg，乙桶油重80kg，从甲桶油里取出多少千克油放入乙桶，才能使甲、乙两桶油的质量比是7：11？
<gadget id="calculator">100 + 80</gadget>
<output>180</output>

<gadget id="calculator">11 + 7</gadget>
<output>18</output>

<gadget id="calculator">180 / 18</gadget>
<output>10</output>

<gadget id="calculator">10 * 7</gadget>
<output>70</output>

<gadget id="calculator">100 - 70</gadget>
<output>30</output>

<result>30</result>