Xiaolan has been reading a 320-page children's encyclopedia for 8 days, 21 pages a day, how many pages are left?
小兰看一本320页的儿童百科全书，已经看了8天，每天看21页，还剩下多少页没有看？
<gadget id="calculator">21 * 8</gadget>
<output>168</output>

<gadget id="calculator">320 - 168</gadget>
<output>152</output>

<result>152</result>