#### Answer

13.5 minutes

#### Work Step by Step

We can represent the wasted water as $x$ and the minutes as $y$.
$x=3y$ because one cup is wasted every 3 minutes.
We want to know what $y$ will be if $x$ is multiplied by 4.5 (4.5 cups wasted). So, we multiply $3y$ by 4.5.
$4.5x=13.5y$
So, it takes 13.5 minutes to waste 4.5 cups of water.