Xiao Ming bought three sets of the same storybook, paid the salesperson 30 yuan, and got back 1.8 yuan. How much is each set of storybooks?
小明买了三套同样的故事书，付给售货员30元，结果找回1.8元，每套故事书多少元？
<gadget id="calculator">30 - 1.8</gadget>
<output>28.2</output>

<gadget id="calculator">28.2 / 3</gadget>
<output>9.4</output>

<result>9.4</result>