#### Answer

$y=\frac{1}{3}x-\frac{14}{3}$

#### Work Step by Step

We are trying to isolate $y$ in the equation $1.5x-4.5y=21$
We subtract $1.5x$ from each side of the equation: $-4.5y=-1.5x+21$
We divide by $-4.5$ on each side of the equation: $y=\frac{-1.5}{-4.5}x+\frac{21}{-4.5}$
We simplify the fractions: $y=\frac{1}{3}x-\frac{14}{3}$