When two numbers are subtracted, the subtrahend remains the same, but the minuend is reduced by 16, what is the difference?
两个数相减，减数不变，被减数减少16，差多少．
<gadget id="calculator">20 - 2</gadget>
<output>18</output>

<gadget id="calculator">20 - 16</gadget>
<output>4</output>

<gadget id="calculator">4 - 2</gadget>
<output>2</output>

<gadget id="calculator">18 - 2</gadget>
<output>16</output>

<result>16</result>