You may have forgotten to distribute the 8 on the right side. This would give you the incorrect equation $\displaystyle{12}{x}-{7}+{5}{x}={16}{x}+{1}+{x}-{8}\usepackage{cmbright}\Huge\$ . The right side should be $\displaystyle{16}{x}+{8}+{x}-{8}\usepackage{cmbright}\Huge\$ . The correct answer is that there is no solution.