If you would like to know how many pages can Henry write in 8 hours, you can calculate this using the following steps:
5 1/4 = 21/4 pages ... 3 hours
x pages = ? ... 8 hours
21/4 * 8 = 3 * x
21 * 2 = 3 * x
3 * x = 42
x = 42 / 3
x = 14 pages
Henry can write 14 pages of his novel in 8 hours.