Xiaoming rides a bicycle from city A to city B at a speed of 20 kilometers per hour, while Xiaoqiang drives from city B to city A at a speed of 15 kilometers per hour. If there is a bird that starts at the same time as them at a speed of 30 kilometers per hour, and starts from city A, and when it meets another person, it returns to fly in the opposite direction, and then flies back and forth between the two in turn, Until they meet, if the distance between AB and AB is 14 kilometers, how many kilometers did the bird fly?
小明骑自行车以每小时20公里的速度由A城市直奔B城市，同时小强以每小时15公里的速度由B开往A．如果有一只鸟，以30公里每小时的速度与他们同时起动，并且从A城市出发，碰到另一个人时就按相反的方向返回去飞，就这样依次在两人之间来回地飞，直到他们相遇，如果AB相距14公里，那么这只小鸟飞行了多少公里．
<gadget id="calculator">20 + 15</gadget>
<output>35</output>

<gadget id="calculator">14 / 35</gadget>
<output>2/5 = around 0.4</output>

<gadget id="calculator">(2/5) * 30</gadget>
<output>12</output>

<result>12</result>