bookshelf has two floors. The number of books on the first floor is 1.5 times that of the second floor. If you take 15 books from the first floor to the second floor, then there are as many books on the two floors. How many books are there on the first floor?
一个书架有两层，第一层的书是第二层的1.5倍，如果从第一层拿15本书到第二层，那么两层的书就一样多，第一层有多少本书？
<gadget id="calculator">15 + 15</gadget>
<output>30</output>

<gadget id="calculator">1.5 - 1</gadget>
<output>0.5</output>

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

<gadget id="calculator">60 * 1.5</gadget>
<output>90</output>

<result>90</result>