There are 30 small birds on the three trees, 2 birds from the first tree fly to the second tree, 3 birds from the second tree fly to the first tree, and 4 birds fly to the first tree On the third tree. 3 from the third tree flew to the first tree, and 2 flew to the second tree. At this time, the birds on the three trees are equal. How many birds were there on the second tree?
三棵树上共有30只小鸟，第一棵树上有2只小鸟飞到第二棵树上，第二棵树上有3只飞到第一棵树上，又有4只飞到第三棵树上．第三棵树上有3只飞到第一棵树上，又有2只飞到第二棵树上．这时三棵树上的小鸟相等，第二棵树上原来有多少只小乌？
<gadget id="calculator">30 / 3</gadget>
<output>10</output>

<gadget id="calculator">10 - 2</gadget>
<output>8</output>

<gadget id="calculator">4 - 2</gadget>
<output>2</output>

<gadget id="calculator">8 + 3 + 2</gadget>
<output>13</output>

<result>13</result>