The east and west cities are 30 kilometers apart. Lingling and Daming set off from the east city to the west city at the same time. Daming is 12 kilometers faster than Lingling per hour. Daming returned immediately after arriving in Xicheng, and met Lingling after a total of 2 hours. How far was Daming from Dongcheng when they met?
东西两城相距30千米，玲玲和大明同时从东城出发往西城走去．大明每小时比玲玲快12千米．大明到达西城后立即返回，共经过2小时与玲玲相遇．相遇时大明距东城多远？
<gadget id="calculator">2 / 2</gadget>
<output>1</output>

<gadget id="calculator">30 * 1</gadget>
<output>30</output>

<gadget id="calculator">30 - 12</gadget>
<output>18</output>

<gadget id="calculator">18 / 2</gadget>
<output>9</output>

<gadget id="calculator">9 * 2</gadget>
<output>18</output>

<result>18</result>