Xiao Ming borrowed a 180-page fable book, he reads 21 pages every day, how many pages are left after 7 days?
小明借了一本180页的寓言故事书，他每天看21页，7天后还剩多少页没有看？
<gadget id="calculator">21 * 7</gadget>
<output>147</output>

<gadget id="calculator">180 - 147</gadget>
<output>33</output>

<result>33</result>