Correct. Using deductive reasoning, you can substitute $\displaystyle{x}={7}\usepackage{cmbright}\Huge\$ into the equation $\displaystyle{x}+{y}={18}\usepackage{cmbright}\Huge\$ , rewrite it as $\displaystyle{7}+{y}={18}\usepackage{cmbright}\Huge\$ , and find that $\displaystyle{y}={11}\usepackage{cmbright}\Huge\$ . This means that the solution set is $\displaystyle{\left({7},{11}\right)}\usepackage{cmbright}\Huge\$ . Since the lines intersect at only one point because their slopes are different, they can not both go through the origin if they are already both going through the point $\displaystyle{\left({7},{11}\right)}\usepackage{cmbright}\Huge\$ .