80 books to 64 books percent change

64 to 80⬇

((64 - 80 / 64)) * 100 = 25 %

Therefore, your answer would have to be: 25% since it increased

Or you can try going with this method as well

80 to 64 ⬇

((80 - 64 / 80)) * 100 = - 20%

Therefore, for that method your answer would be-20% because it decreased

A change from 64 to 80 represents a positive change (increase) of 25%