You may have made two mistakes. While trying to get the constant terms together on the right side, you may have added 1 to 13. To combine the constant terms, you would need to subtract 1 from both sides. While trying to get the variable terms together on the left side, you may have added x to $\displaystyle{4}{x}\usepackage{cmbright}\Huge\$ . To combine the variable terms, you would need to subtract x from both sides.