[tex]\displaystyle\bf\\\left \{ {{5x-10=y} \atop {3x+9=12y+36} \ |:3} \right.\\\\\\\left \{ {{5x-10=y} \atop {x+3=4y+12}} \right.\\\\\\\left \{ {{y=5x-10} \atop {x+3=4\cdot(5x-10)+12}} \right. \\\\\\\left \{ {{y=5x-10} \atop {x+3=20x-40+12}} \right. \\\\\\\left \{ {{y=5x-10} \atop {x-20x=-28-3}} \right.\\\\\\\left \{ {{y=5x-10} \atop {-19x=-31}} \right. \\\\\\\left \{ {{x=1\dfrac{12}{19} } \atop {y=5\cdot1\dfrac{12}{19} -10}} \right.[/tex]

[tex]\displaystyle\bf\\\left \{ {{x=1\dfrac{12}{19} } \atop {y=8\dfrac{3}{19} -10}} \right. \\\\\\\left \{ {{x=1\dfrac{12}{19} } \atop {y=-1\dfrac{16}{19} }} \right. \\\\\\Otvet \ : \ \Big(1\frac{12}{19} \ ; \ -1\frac{16}{19} \Big)[/tex]