First, let's find how many page's Greta read per day. She read a total of 900 pages across 15 days, so she read:
900 pages / 15 days = 60 pages/day
Now we can find how many pages she read per hour by dividing the 60 pages per day by 5 hours:
60 / 5 = 12 pages/hour
The answer is 12 pages.