Answer
$\frac{31}{45y}$
Work Step by Step
By inspection, we see that the LCM of the denominators is $18y$. Therefore, we create a denominator using this LCM and obtain:
$\frac{11}{9y}-\frac{8}{15y}$
=$\frac{5(11)-3(8)}{45y}$
=$\frac{55-24}{45y}$
=$\frac{31}{45y}$