Correct. The area of the blanket is $\displaystyle{5}\cdot{6}={30}\usepackage{cmbright}\Huge\$ . Adding a border of width x, the new area of the blanket is $\displaystyle{\left({5}+{2}{x}\right)}{\left({6}+{2}{x}\right)}\usepackage{cmbright}\Huge\$ , since the width x is added to both the left and right sides and the top and bottom of the blanket. The area of the border is thus given by the difference between the area of the blanket with the border and the area of the blanket without the border, or $\displaystyle{\left({5}+{2}{x}\right)}{\left({6}+{2}{x}\right)}-{\left({5}\right)}{\left({6}\right)}={12}\usepackage{cmbright}\Huge\$ .