The minuend increases by 15, and the subtrahend decreases by 15. What is the difference [fill in: how much to increase or decrease].
被减数增加15，减数减少15，差多少【填：增加或者减少多少】．
<gadget id="calculator">115 - 35</gadget>
<output>80</output>

<gadget id="calculator">100 - 50</gadget>
<output>50</output>

<gadget id="calculator">80 - 50</gadget>
<output>30</output>

<result>30</result>