A box of apples weighs 21.5 kilograms, half of which is eaten, and the weight of the box is still 11.5 kilograms. How many kilograms does the box weigh?
一箱苹果连箱重21.5千克，吃了一半，连箱重还有11.5千克，箱重多少千克．
<gadget id="calculator">21.5 - 11.5</gadget>
<output>10</output>

<gadget id="calculator">10 * 2</gadget>
<output>20</output>

<gadget id="calculator">21.5 - 20</gadget>
<output>1.5</output>

<result>1.5</result>