Answer :
[tex] \left \{ {{x+2y=14} \atop {y=3x-14}} \right.\\\\Substitution\\\\
x+2(3x-14)=14\\
x+6x-28=14\\
7x-28=14\ \ \ | add\ 28\\
7x=42\ \ \ | divide\ by\ 7\\x=6\\
y=3x-14=3*6-14=18-14=4\\\\Solution:\\ \left \{ {{y=4} \atop {x=6}} \right. [/tex]