There are 987 children's books in the library, lent to 18 classes, 46 books per class, how many books are left?
图书室有少儿读物987本，借给18个班，每班46本，还剩多少本？
<gadget id="calculator">46 * 18</gadget>
<output>828</output>

<gadget id="calculator">987 - 828</gadget>
<output>159</output>

<result>159</result>