Take care of your brain. . it's the only one you've got.
If the book was 30 pages long, it would take you 1 hour to read it.
If the book was 60 pages long, it would take you 2 hours to read it because there are two 30's in 60, or 60 divided by 30 is 2.
If the book was 90 pages long, it would take you 1 hour for the first 30 pages, another hour for the next 30 pages, and another hour for the last 30 pages or 3 hours. 90 divided by 30 is 3.
I think you can solve the problem now without affecting your brain.