Answer
$-\frac{5}{6y}$
Work Step by Step
First, we multiply the numerators by each other and the denominators by each other:
$\frac{10x}{-9y}\times\frac{15}{20x}=-\frac{10x\times15}{9y\times20x}=-\frac{150x}{180xy}$
Next, we simplify the resultant expression to obtain the answer:
$-\frac{150x}{180xy}=-\frac{150}{180y}=-\frac{15}{18y}=-\frac{5}{6y}$
