Xiaoqiang’s original number of story books was three times that of Xiaogang’s and 8 less than Xiaogang’s. Later, Xiaoqiang bought 15 more, and Xiaogang bought another 12. As a result, Xiaoqiang’s books were twice as many as Xiaogang’s and 4 more. Just how many books?
小强原有故事书的本数是小刚的3倍少8本，后来小强又买来15本，小刚又买来12本，结果小强的书是小刚的2倍多4本，那么原来小刚有多少本书？
<gadget id="calculator">12 * 2</gadget>
<output>24</output>

<gadget id="calculator">4 - 15</gadget>
<output>-11</output>

<gadget id="calculator">8 + 24 + (-11)</gadget>
<output>21</output>

<gadget id="calculator">3 - 2</gadget>
<output>1</output>

<gadget id="calculator">21 / 1</gadget>
<output>21</output>

<result>21</result>