You may have forgotten to distribute the 2 on the left side of the equation and tried to solve the incorrect equation $\displaystyle{4}{x}-{1}+{10}={9}+{9}{x}-{5}{x}\usepackage{cmbright}\Huge\$ . The left side should be $\displaystyle{4}{x}-{2}+{10}\usepackage{cmbright}\Huge\$ .