Chapter 2 - Functions, Equations, and Graphs - 2-2 Direct Variation - Practice and Problem-Solving Exercises - Page 71: 26

13.5 minutes

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.