Xiaomin reads a 310-page book. He reads an average of 20 pages a day in the first 3 days, and then 25 pages a day. How many days can he finish it?
小敏看310页的书，前3天平均每天看20页，以后每天看25页，再用几天可以看完？
<gadget id="calculator">20 * 3</gadget>
<output>60</output>

<gadget id="calculator">310 - 60</gadget>
<output>250</output>

<gadget id="calculator">250 / 25</gadget>
<output>10</output>

<result>10</result>