To find the total cost \( c \) Vicky paid for the oranges, we can use the equation:
\[ c = \text{(cost per pound)} \times \text{(number of pounds)} \]
In this case, the cost per pound is $3.90 and the number of pounds is \( 3\frac{1}{2} \) or \( 3.5 \).
So, the equation becomes:
\[ c = 3.90 \times 3.5 \]
Calculating the total cost:
\[ c = 3.90 \times 3.5 = 13.65 \]
Thus, the equation that represents the total cost Vicky paid is not explicitly among the options, but one of the options represents the relationship incorrectly.
We check the responses to find the closest match:
- \( 3.90c = 3.5 \); Vicky paid $0.90. - Incorrect
- \( c/3.5 = 3.90 \); Vicky paid $13.65. - This is an incorrect representation of the cost calculation but gives the right total.
- \( c/3.90 = 3.5 \); Vicky paid $1.11. - Incorrect
- \( 3.90/3.5 = c \); Vicky paid $13.65. - incorrect setup.
The correct format should be \( c = 3.90 \times 3.5 \) or stated as \( c = 13.65 \). Since the interpretation \( c/3.5 = 3.90 \) implies that you would multiply by 3.5 to get cost, and \( 3.90 \) is the price per pound, this equation \( c = 3.90 \times 3.5 \) leads directly to \( c = 13.65 \).
The most valid option that approaches this concept (despite the incorrect structure) would be:
Option 2 (or the one closest):
\( \frac{c}{3.5} = 3.90; \) Vicky paid $13.65.
Thus, the option that gives the total Vicky paid correctly is the second one because it derives a similar relationship through the cost per pound and utilizes the amounts accordingly.