Correct. If $\displaystyle{3}{x}-{y}={6}\usepackage{cmbright}\Huge\$ , then $\displaystyle{3}{x}-{6}={y}\usepackage{cmbright}\Huge\$ and this line (also called $\displaystyle{y}={3}{x}-{6}\usepackage{cmbright}\Huge\$ ) has slope 3. Since the line $\displaystyle{y}=-{3}{x}+{19}\usepackage{cmbright}\Huge\$ has slope -3, the two lines are not parallel.