Wang Ming reads a 120-page book. He reads an average of 15 pages a day in the first 4 days, and he needs to finish the rest within 3 days. How many pages do he need to read in an average day?
王明看一本120页的书，前4天平均每天看15页，剩下的需在3天内看完，平均每天要看多少页？
<gadget id="calculator">15 * 4</gadget>
<output>60</output>

<gadget id="calculator">120 - 60</gadget>
<output>60</output>

<gadget id="calculator">60 / 3</gadget>
<output>20</output>

<result>20</result>