Subtract $\displaystyle{3}{k}\usepackage{cmbright}\Huge\$ from both sides: $\displaystyle{l}-{3}{k}={14}{j}\usepackage{cmbright}\Huge\$

Divide both sides by 14: $\displaystyle\frac{{{l}-{3}{k}}}{{14}}=\frac{{{14}{j}}}{{14}}\usepackage{cmbright}\Huge\$

Simplify: $\displaystyle\frac{{{l}-{3}{k}}}{{14}}={j}\usepackage{cmbright}\Huge\$