Correct. Add the first and second equations: $\displaystyle{2}{e}+{f{=}}{1}\usepackage{cmbright}\Huge\$

Add the first and third equations: $\displaystyle-{2}{e}-{4}{f{=}}{8}\usepackage{cmbright}\Huge\$

Add these two new equations: $\displaystyle-{3}{f{=}}{9}\usepackage{cmbright}\Huge\$ , so $\displaystyle{f{=}}-{3}\usepackage{cmbright}\Huge\$

Substitute this into the first new equation: $\displaystyle{2}{e}-{3}={1}\usepackage{cmbright}\Huge\$ , so $\displaystyle{e}={2}\usepackage{cmbright}\Huge\$ .

Substitute e and f into the first original equation: $\displaystyle{4}{d}-{6}-{6}={4}\usepackage{cmbright}\Huge\$ , so $\displaystyle{d}={4}\usepackage{cmbright}\Huge\$

Check the values of e, d, and f in all three original equations.