3x + y = 12 ,\\ -3x+5y=24.

[tex]\displaystyle\bf\\ + \left \{ {{3x + y = 12} \atop { - 3x + 5y = 24 }} \right. \\ \\ y + 5y = 24 + 12 \\ 6y = 36 \\ y = 36 \div 6 \\ y = 6 \\ \\ 3x + 6 = 12 \\ 3x = 12 - 6 \\ 3x = 6 \\ x = 6 \div 3 \\ x = 2[/tex]

Ответ: ( 2 ; 6 )