To create an equation that represents the total cost \( c \) of \( w \) ounces of granola, we can start by noting that the total cost is proportional to the weight. This means we can express the relationship using the equation:
\[ c = k \cdot w \]
where \( k \) is the constant of proportionality (cost per ounce).
From the information provided, we know that the total cost of 8 ounces of granola is $3.12. We can use this information to find the value of \( k \):
\[ 3.12 = k \cdot 8 \]
To find \( k \), we divide both sides by 8:
\[ k = \frac{3.12}{8} = 0.39 \]
Now that we have found \( k \), we can substitute it back into the equation for total cost:
\[ c = 0.39 \cdot w \]
Thus, the equation that represents the total cost \( c \) of \( w \) ounces of granola is:
\[ c = 0.39w \]