A snail crawls forward 25 cm, then retreats 15 cm, and then crawls forward 10 cm, how many cm does it advance?
一只蜗牛向前爬25厘米，又朝后退15厘米，在朝前爬10厘米，结果前进了多少厘米．
<gadget id="calculator">25 - 15</gadget>
<output>10</output>

<gadget id="calculator">10 + 10</gadget>
<output>20</output>

<result>20</result>