Answer:
She hasn't read 35% of the book
Explanation:
1st way: Since 80 pages represent 100%
52 pages represent 100 * 52 / 80 = 65% pages read
100 - 65 = 35 pages page not read.
2nd way: 80 - 52 = 28 pages not read
28 pages represent 100 * 28 / 80 = 35% pages not read