A bookstore wants to send 980 mathematics experiment textbooks to the experimental area. If each box contains 50 books, 18 boxes have already been packed. How many books are left unpacked?
某书店要把980本数学实验教材送到实验区去，如果每箱装50本，已经装了18箱，还有多少书没有装箱？
<gadget id="calculator">50 * 18</gadget>
<output>900</output>

<gadget id="calculator">980 - 900</gadget>
<output>80</output>

<result>80</result>