4 hours
Jaquan can read 1/16 of a book in 1/2 an hour, so he can read 2/16 or 1/8 of a book in one hour (multiplying both by 2). Since we are looking for when he finishes half the book (1/2 or 4/8), we are looking for how many hours it takes at a rate of 1/8 books/hr to read 4/8 of a book.
Thus, 1/8x = 4/8, solved for x = 4
