ship travels between ports A and B. It takes 12 hours for the ship to travel along the current, and 15 hours to travel against the current. On this day, the speed of the water increases for some reason. The ship only needs 10 hours to travel along the current. How long does it take for the boat to travel upstream on this day?
某船往返于A、B两港之间，船顺水走完全程需12小时，逆水走完全程需要15小时，这天因故使水速加大，该船顺水走完全程只需10小时，问这天该船逆水而上走完全程需多长时间？
<result>20</result>