"Subtract 50 and add 20" from 2100, this is called an operation, after how many operations, the result is 0.
从2100里"减去50，再加上20"，这称作一次操作，经过多少次操作，所得的结果是0．
<gadget id="calculator">50 - 20</gadget>
<output>30</output>

<gadget id="calculator">2_100 / 30</gadget>
<output>70</output>

<result>70</result>