The sum of the minuend, the subtrahend and the difference is 120, and the subtrahend is 40. What is the difference?
被减数、减数与差的和是120，减数是40，差是多少．
<gadget id="calculator">120 / 2</gadget>
<output>60</output>

<gadget id="calculator">60 - 40</gadget>
<output>20</output>

<result>20</result>