If you read 60 pages of a book every day, then you can’t finish it in 4 days, and you have more than 5 days; if you read 70 pages a day, you can’t finish it in 3 days, but you have more than 4 days; if you read x pages a day, you can finish it in exactly x days (x is a natural number), how many pages does this book have.
一本书如果每天读60页，那么4天读不完，5天又有余；如果每天读70页，那么3天读不完，4天又有余；如果每天读x页，恰好x天读完(x是自然数)，这本书有多少页．
<gadget id="calculator">16 * 16</gadget>
<output>256</output>

<result>256</result>