In one hour, Diep will read for 1/4 hour x 4 = 1 full hour.
In 1/4 of an hour, Diep read 1/6 of the book.
To find out how much he can read in 1 hour, we need to multiply both the numerator and denominator by the same number to keep the fraction equivalent. We can multiply 1/6 by 4/4 to get:
1/6 x 4/4 = 4/24
Therefore, Diep can read 4/24 of the book in 1 hour, or simplified, 1/6 of the book.