There are 9 boxes of books in the library, 180 books in each box, 620 books have been borrowed, how many books are left?
图书室有9箱图书，每箱180本，借出去了620本，还剩多少本．
<gadget id="calculator">180 * 9</gadget>
<output>1_620</output>

<gadget id="calculator">1_620 - 620</gadget>
<output>1_000</output>

<result>1_000</result>