Swallows can eat about 690 pests in 3 days, and frogs can eat about 210 pests per day. How many more pests can swallows eat per day than frogs?
燕子3天大约能吃掉690只害虫，青蛙每天大约能吃掉210只害虫，燕子比青蛙每天大约多吃多少只害虫？
<gadget id="calculator">690 / 3</gadget>
<output>230</output>

<gadget id="calculator">230 - 210</gadget>
<output>20</output>

<result>20</result>