To model the total amount of water \( w \) that Martina used in her science project, you can represent it with the formula:
\[ w = 8.5 \times n \]
where \( n \) is the number of containers. Since Martina used 5 containers, you can substitute \( n \) with 5:
\[ w = 8.5 \times 5 \]
Now, calculating that gives:
\[ w = 42.5 \text{ ounces} \]
So, the equation that models the total amount of water \( w \) is:
\[ w = 8.5 \times 5 \]
And the total amount of water Martina used is 42.5 ounces.