Step-by-step explanation:
[tex]\left\{\begin{array}{ccc}x-7y=4&\text{multiply both sides by 3}\\-3x+21y=5\end{array}\right\\\underline{+\left\{\begin{array}{ccc}3x-21y=12\\-3x+21y=5\end{array}\right}\qquad\text{add both sides of the equations}\\.\qquad\qquad0=17\qquad\bold{FALSE}\\\\\bold{CONCLUSION:}\ \bold{no\ solutions}\\\\\text{What do you know about the two lines in the system of equations? }\\\\\text{The lines do not have a common point (s).}\\\text{They don't intersect. Therefore, they are parallel lines.}[/tex]
