Answer:
[tex]\large\boxed{x=-\dfrac{3}{2},\ y=-3\to\left(-\dfrac{3}{2},\ -3\right)}[/tex]
Step-by-step explanation:
[tex]\left\{\begin{array}{ccc}-6x-4y=21\\-6x+3y=0&\text{change the signs}\end{array}\right\\\underline{+\left\{\begin{array}{ccc}-6x-4y=21\\6x-3y=0\end{array}\right}\qquad\text{add both sides of the equations}\\.\qquad-7y=21\qquad\text{divide both sides by (-7)}\\.\qquad\boxed{y=-3}\\\\\text{Put the value of}\ y\ \text{to the second equation}\ 6x-3y=0:\\\\6x-3(-3)=0\\6x+9=0\qquad\text{subtract 9 from both sides}\\6x=-9\qquad\text{divide both sides by 6}\\x=-\dfrac{9:3}{6:3}\\\boxed{x=-\dfrac{3}{2}}[/tex]
