The school bought 165 science and technology books, and the number of science and technology books is 21 more than three times that of story books. How many story books did you buy?
学校买来165本科技书，科技书的本数比故事书的3倍多21本．买来故事书多少本？
<gadget id="calculator">165 - 21</gadget>
<output>144</output>

<gadget id="calculator">144 / 3</gadget>
<output>48</output>

<result>48</result>