[tex] \left \{ {{4x-7y=3} \atop {x-7y=15}} \right. \\\\
\left \{ {{4x-7y=3} \atop {x=15+7y}} \right. \\\\ substitution\ method\\\\
4*(15+7y)-7y=3\\\\
60+28y-7y=3\\\\
60+21y=3\ \ \ \ | subtract\ \\\\
21y=-57\\\\
y=-\frac{57}{21}=-\frac{19}{7}\\\\
x=15+7*(-\frac{19}{7})=15-19=-4\\\\\ Solution :\ \left \{ {{y=-\frac{19}{7}} \atop {x=-4}} \right. [/tex]
