During the period from January to June 2013, Uncle Wang received a total of 270 emails, of which the ratio of ordinary mails to emails was 2:7. How many emails did he receive?
王叔叔在2013年1月～6月期间，共收到邮件270封，其中普通邮件和电子邮件的比是2：7，他收到电子邮件多少封．
<gadget id="calculator">2 + 7</gadget>
<output>9</output>

<gadget id="calculator">270 / 9</gadget>
<output>30</output>

<gadget id="calculator">30 * 7</gadget>
<output>210</output>

<result>210</result>