Correct. The area of the flag is $\displaystyle{20}\cdot{12}={240}\usepackage{cmbright}\Huge\$ . Adding a border of width x, the new area of the flag is $\displaystyle{\left({20}+{2}{x}\right)}{\left({12}+{2}{x}\right)}\usepackage{cmbright}\Huge\$ . The area of the border is thus given by the difference between the area of the flag with the border and the area of the flag without the border, or $\displaystyle{\left({20}+{2}{x}\right)}{\left({12}+{2}{x}\right)}-{\left({20}\right)}{\left({12}\right)}={228}\usepackage{cmbright}\Huge\$ .