From 86 books to 150 books. An increase of 64 books.
(150 - 86) / 86 = 64 / 86 = 0.744 * 100% = 74.40% or 74% increase
150 / 86 = 1.744 * 100% = 174.40%
86 is the basis. It is 100%
If the problem asks for the value of the percentage increase and the rate is given 74.4% of 86. Then 86 * 74.4% = 64. You just add 64 to 86 to get the new total of books which is 150.
