To find the total cost \( c \) that Vicky paid for the oranges, we can use the equation:
\[ c = (3.5 \text{ pounds}) \times (3.90 \text{ dollars per pound}) \]
Calculating the total cost:
\[ c = 3.5 \times 3.90 = 13.65 \]
The correct equation that represents the total cost is:
\[ c = 3.5 \times 3.90 \]
This means that \( c = 13.65 \). Thus, the response that corresponds to this calculation is:
c = 3.90/3.5; Vicky paid $13.65.
This corresponds to correctly stating the total cost and value for \( c\).