Take 10 more books than 25% of the total number from the bookshelf. At this time, there are 10 more books left on the bookshelf than the ones taken away. How many books are there on the bookshelf?
从书架上拿出总数的25%多10本，这时书架上剩下的书比拿走的多10本．书架上原来有多少本书．
<gadget id="calculator">10 + 20</gadget>
<output>30</output>

<gadget id="calculator">0.75 - 0.25</gadget>
<output>0.5</output>

<gadget id="calculator">30 / 0.5</gadget>
<output>60</output>

<result>60</result>