A frog eats 100 pests every day, which is 20 less than three times that of a swallow. How many pests does a swallow eat every day?
一只青蛙每天吃100只害虫，比一只燕子吃的3倍少20只，一只燕子每天吃多少只害虫？
<gadget id="calculator">100 + 20</gadget>
<output>120</output>

<gadget id="calculator">120 / 3</gadget>
<output>40</output>

<result>40</result>