There are 20 birds on the tree, 7 flew away in the first time, and 9 flew away in the second time, how many birds flew away in total?
树上有20只小鸟，第一次飞走了7只，第二次飞走了9只，两次一共飞走了多少只小鸟？
<gadget id="calculator">7 + 9</gadget>
<output>16</output>

<result>16</result>