The mass of a box of pears is 41.5 kilograms. After taking out half of the box, the mass of the box is 21.5 kilograms. How many kilograms is the mass of the box?
一箱梨连箱的质量是41.5千克，拿出一半后，连箱的质量是21.5千克，箱了的质量是多少千克？
<gadget id="calculator">41.5 - 21.5</gadget>
<output>20</output>

<gadget id="calculator">20 * 2</gadget>
<output>40</output>

<gadget id="calculator">41.5 - 40</gadget>
<output>1.5</output>

<result>1.5</result>