[tex]\displaystyle\bf\\\left \{ {{3x +ay = 8 \: \: | \times 4} \atop {12x - 12y = 32 }} \right. \\ \displaystyle\bf\\\left \{ {{12x +4 ay = 32} \atop {12x - 12y = 32 }} \right. \\ \\ 4a = - 12 \\ a = - 12 \div 4 \\ a = - 3[/tex]

Ответ: Б) - 3