The fourth grade donated 600 books to Hope Primary School. Every 45 books were packed into a pack, and 13 packs were packed. How many books are left unpacked?
四年级为希望小学捐赠了600本书，每45本包成一包，包了13包，还剩下多少本没包？
<gadget id="calculator">45 * 13</gadget>
<output>585</output>

<gadget id="calculator">600 - 585</gadget>
<output>15</output>

<result>15</result>