It’s winter vacation, and uncle gave Qiangqiang a book with many stories. Qiangqiang plans to read the same number of stories every day, and he can read them in 20 days. But Qiangqiang found the stories very interesting while reading the book, actually read 3 more stories every day than originally planned, and ended up finishing the story book 4 days earlier. How many stories are there in this storybook?
放寒假了，叔叔送给强强一本有许多个故事的书，强强计划每天看同样个数的故事，用20天可看完．但强强在看书时发现故事很有趣，实际每天比原计划多看3个故事，结果提前4天看完了故事书．这本故事书一共有多少个故事．
<gadget id="calculator">20 - 4</gadget>
<output>16</output>

<gadget id="calculator">16 / 4</gadget>
<output>4</output>

<gadget id="calculator">3 * 4 * 20</gadget>
<output>240</output>

<result>240</result>