Aunt Wang sold 12 kilograms of eggs in the morning and 18 kilograms in the afternoon, which was 55.2 yuan more in the afternoon than in the morning. How much is the average price per kilogram of eggs?
王大妈卖鸡蛋，上午卖了12千克，下午卖了18千克，下午比上午多卖了55.2元．平均每千克鸡蛋卖多少元？
<gadget id="calculator">18 - 12</gadget>
<output>6</output>

<gadget id="calculator">55.2 / 6</gadget>
<output>9.2</output>

<result>9.2</result>