Answer
$\frac{1}{24y}$.
Work Step by Step
In order to add or subtract fractions, we start by making a common denominator (bottom of the fraction). Thus, we multiply 3/8y by 3/3 and 5/12y by 2/2 to obtain:
$\frac{10}{24y}$-($\frac{9}{24y}$)=$\frac{1}{24y}$.