Xiao Ming reads a 420-page book for a week, and reads an average of 45 pages a day. How many pages are left?
一本420页的书，小明看了一周，平均每天看45页，还剩多少页没有看？
<gadget id="calculator">45 * 7</gadget>
<output>315</output>

<gadget id="calculator">420 - 315</gadget>
<output>105</output>

<result>105</result>