Suiyang Middle School used 150 rounds of bullets for the first time, twice as many bullets for the second time, and 210 rounds for the third time. How many bullets are used on average each time?
绥阳中学进行军事训练，第一次用子弹150发，第二次用的是第一次的2倍，第三次用子弹210发．平均每次用子弹多少发？
<gadget id="calculator">150 * 2</gadget>
<output>300</output>

<gadget id="calculator">150 + 300 + 210</gadget>
<output>660</output>

<gadget id="calculator">660 / 3</gadget>
<output>220</output>

<result>220</result>