You may have subtracted not only the 7, but also the $\displaystyle{5}{x}\usepackage{cmbright}\Huge\$ on the left side, which would be the incorrect order of operations. This would give you $\displaystyle{7}{x}-{7}\usepackage{cmbright}\Huge\$ on the left side, but it should be $\displaystyle{17}{x}-{7}\usepackage{cmbright}\Huge\$ . The correct answer is that there is no solution.