The school bought a total of 210 books of three kinds, among which science books are three times more than art books, and story books are 10 more than art books. How many story books did the school buy?
学校买来三种书共210本，其中科技书是文艺书的3倍，故事书比文艺书多10本，学校买来故事书多少本．
<gadget id="calculator">210 - 10</gadget>
<output>200</output>

<gadget id="calculator">1 + 3 + 1</gadget>
<output>5</output>

<gadget id="calculator">200 / 5</gadget>
<output>40</output>

<gadget id="calculator">40 + 10</gadget>
<output>50</output>

<result>50</result>