#### Answer

$\frac{7y}{36}$

#### Work Step by Step

$9=\underline3\times\underline3$
$12=\underline2\times\underline2\times3$
$lcd=2\times2\times3\times3=36$
$\frac{5y}{12}-\frac{2y}{9}=\frac{5y\times3}{12\times3}-\frac{2y\times4}{9\times4}=\frac{15y}{36}-\frac{8y}{36}=\frac{15y-8y}{36}=\frac{7y}{36}$