Correct. Multiply the second equation by 3: $\displaystyle-{9}{r}-{9}{s}-{3}{t}=-{36}\usepackage{cmbright}\Huge\$

Add the first equation to get: $\displaystyle-{7}{r}-{5}{s}=-{25}\usepackage{cmbright}\Huge\$

Multiply the first equation by 2: $\displaystyle{4}{r}+{8}{s}+{6}{t}={22}\usepackage{cmbright}\Huge\$

Add the third equation to get: $\displaystyle{7}{r}+{6}{s}={23}\usepackage{cmbright}\Huge\$

Add the two new equations: $\displaystyle{s}=-{2}\usepackage{cmbright}\Huge\$

Substitute into the previous equation: $\displaystyle{7}{r}-{12}={23}\usepackage{cmbright}\Huge\$ , so $\displaystyle{r}={5}\usepackage{cmbright}\Huge\$

Use these values to find t and check your solution in all three equations.