So, what is nine twenty-fifths? let's write it down as a fraction:

now, what happens if we multiply both nominator and the demominator by the same number? the value remains the same!
so let's multiply it by 4:

one of the ways of reading this fraction is: 36 out of 100, so this is almost the answer: 36 students didn't like the book.
And the remainder, 100-36=64 did like it!