#### Answer

$\frac{1}{18y}$

#### 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:
$\frac{5}{6y}-\frac{7}{9y}$
=$\frac{3(5)-2(7)}{18y}$
=$\frac{15-14}{18y}$
=$\frac{1}{18y}$