There are 4 bookcases in Mr. Li's house, with 9 floors in total, and 25 books are placed on each floor. How many books does Mr. Li have in total?
李老师家有4个书柜，共有9层，每层都放了25本书，李老师家共有多少本书？
<gadget id="calculator">4 * 9 * 25</gadget>
<output>900</output>

<result>900</result>