A barrel of peanut oil weighs 28 kilograms. After half of the oil is poured out, the barrel still weighs 15 kilograms. How many kilograms does the barrel weigh?
一桶花生油连桶重28千克，油倒出一半后，连桶还重15千克，桶重多少千克．
<gadget id="calculator">28 - 15</gadget>
<output>13</output>

<gadget id="calculator">15 - 13</gadget>
<output>2</output>

<result>2</result>