Obviously read a 280-page book, and read 120 pages in the first 3 days. According to this calculation, how many days will it take to finish reading? (answer with ratio)
明明看一本280页的书，前3天看了120页，照这样计算，还需几天才能看完？(用比例解答)
<gadget id="calculator">280 - 120</gadget>
<output>160</output>

<gadget id="calculator">120 / 3</gadget>
<output>40</output>

<gadget id="calculator">160 / 40</gadget>
<output>4</output>

<result>4</result>