A 378-page story book, read 21 pages a day for 13 days, and the rest will take a week to read, how many pages should I read at least every day?
一本378页的故事书，每天看21页，看了13天，剩下的要一个星期看完，每天至少看多少页？
<gadget id="calculator">21 * 13</gadget>
<output>273</output>

<gadget id="calculator">378 - 273</gadget>
<output>105</output>

<gadget id="calculator">105 / 7</gadget>
<output>15</output>

<result>15</result>