We know that 7 pounds of potatoes cost $63.
This is a proportional relationship between quantity (pounds of potatoes) and cost.
We can calculate how many pounds of potatoes we can get with $261 applying the Rule of three:
![261\text{ \$}\cdot(\frac{7\text{ pounds}}{63\text{ \$}})=29\text{ pounds}](https://img.qammunity.org/2023/formulas/mathematics/college/m69zp5w9afq3q2fugp7uh3fhfa2avb9ra9.png)
We can buy 29 pounds of potatoes with $261
NOTE: I use the units ($ and pounds) to know how to multiply them in order to get the result I was looking for.