Riley has a farm on a rectangular piece of land that is 200 meters wide

200 meters wide is the answer

Do you mean "Riley has a farm on a rectangular piece of land that is 200 meters wide. This area is divided into two parts: A square area where she grows avocados (whose side is the same as the length of the farm), and the remaining area where she lives.

Every week, Riley spends $3 per square meter on the area where she lives, and earns $7 per square meter from the area where she grows avocados. That way, she manages to save some money every week."?

The answer is 7L^2>3l (200-l)