The answer is 18 pages per day. If you add 36 and 54 you get 90. Since she reads the same everyday over 5 days you can set up equation 5x = 90. Divide each side by 5 yields x = 18. To check, it takes 2 days to read 36 pages and 3 days to read 54 pages for a total of 5 days at 18 pages per day.