At 12:00pm the pool is half covered by the shade of a tree. And by 13:00pm the pool is in full sun. (So that between 12 and 1 pm the pool is partially cover by some shade.) It can be assumed that the shade covers half the pool at 12:30 and so on.
If the pool of water is 28 degree Celsius at 11:50am, how long will it take to increase it 32 degrees Celsius?