Correct. The area of the section on the left is $\displaystyle{20}\text{ft}\cdot{10}\text{ft}={200}{\text{ft}}^{{2}}\usepackage{cmbright}\Huge\$ , and the area of the section on the right is $\displaystyle{10}\text{ft}\cdot{10}\text{ft}={100}{\text{ft}}^{{2}}\usepackage{cmbright}\Huge\$ , so the total is $\displaystyle{200}{\text{ft}}^{{2}}+{100}{\text{ft}}^{{2}}={300}{\text{ft}}^{{2}}\usepackage{cmbright}\Huge\$ .