To find the total cost \( c \) that Vicky paid for the oranges, we can set up the equation based on the cost per pound and the total number of pounds she bought.
Given:
- Cost per pound = $3.90
- Number of pounds = 312
The total cost \( c \) can be calculated using the equation:
\[ c = \text{cost per pound} \times \text{number of pounds} \] \[ c = 3.90 \times 312 \]
Thus, the equation that represents the total cost is:
\[ c = 3.90 \times 312 \]
However, none of the equations presented in your responses accurately represents this relationship or directly computes \( c \).
To clarify, the total cost that she should pay, calculated directly, is:
\[ c = 3.90 \times 312 = 1219.80 \]
It appears the options given in your question do not correctly represent the situation. Please check the options again or restate them so I can assist you further in identifying the correct one.