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

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)

make sure you have version 2.50

try looking in the very back of the book : )

step-by-step explanation:

you can download it here