You read 240 pages in 20 minutes
Let x = amount of time (in minutes) that it takes to read 300 pages
Then, 240/20 = 300/x
12 = 300/x
12x = 300
x = 25 min
So, if you start reading at 10:55 AM, you will finish reading 300 pages 25 minutes later (at 11:20 AM). That's fast reading!
x = 300/240 = 5/4 = 1.25 hours