Shannon paid $57.25 for 28 pounds of potatoes. Shannon estimated the cost per pound to be $3.00. What is her error?

To find Shannon's estimated cost per pound and assess her error, we can perform the following calculations based on her provided information.

First, let's calculate the actual cost per pound of potatoes:

1. **Calculate the actual cost per pound:**
\[
\text{Cost per pound} = \frac{\text{Total cost}}{\text{Total weight}} = \frac{57.25}{28} \approx 2.0464
\]

Next, let’s evaluate each of Shannon's rounding methods to see which one leads her to the estimated cost of $3.00 per pound.

1. **Shannon rounded $57.25 to $40 and 28 pounds to 20:**
\[
\text{Estimated cost per pound} = \frac{40}{20} = 2.00
\]
(Not $3.00)

2. **Shannon rounded $57.25 to $60 and 28 pounds to 20:**
\[
\text{Estimated cost per pound} = \frac{60}{20} = 3.00
\]
(This is correct)

3. **Shannon rounded $57.25 to $40 and 28 pounds to 30:**
\[
\text{Estimated cost per pound} = \frac{40}{30} \approx 1.3333
\]
(Not $3.00)

4. **Shannon rounded $57.25 to $60 and 28 pounds to 40:**
\[
\text{Estimated cost per pound} = \frac{60}{40} = 1.50
\]
(Not $3.00)

From the evaluations, we see that **Shannon rounded $57.25 to $60 and 28 pounds to 20 before dividing**, which led her to estimate the cost per pound to be exactly $3.00.

Since this rounding method produced her estimated value, we can conclude that the error arises from how she rounded the total cost and weight. Her estimate calculations provided the closest approximation to her intended answer ($3.00).

Thus, the correct choice representing her calculation is:
**Shannon rounded $57.25 to $60 and 28 pounds to 20 before dividing.**