A and B have two barrels of oil. A barrel contains 90 kilograms of oil. After pouring out half of it, another 15 kilograms is put into B barrel. At this time, the weight of the two barrels is equal. How many kilograms of oil is there in B barrel?
甲、乙两桶油，甲桶有油90千克，倒去一半后，再拿出15千克到乙桶，这时两桶油重相等，乙桶原有多少千克油．
<gadget id="calculator">90 / 2</gadget>
<output>45</output>

<gadget id="calculator">15 * 2</gadget>
<output>30</output>

<gadget id="calculator">90 - 45 - 30</gadget>
<output>15</output>

<result>15</result>