[tex]\displaystyle\bf\\\left \{ {{ \frac{x}{3} + \frac{y}{4} = 2 \: \: | \times 12 } \atop { \frac{y}{6} - \frac{x}{4} = - \frac{1}{12} \: \: | \times 12}} \right. \\ \displaystyle\bf\\\left \{ {{4x +3 y = 24 \: \: | \times 3 } \atop { - 3x + 2y = - 1 \: \: | \times 4}} \right. \\\displaystyle\bf\\ + \left \{ {{12x + 9y = 72} \atop { - 12x + 8y = - 4 }} \right. \\ \\ 9y + 8y = 72 - 4 \\ 17y = 68 \\ y = 68 \div 17 \\ y = 4 \\ \\ 4x + 3 \times 4 = 24 \\ 4x + 12 = 24 \\ 4x = 24 - 12 \\ 4x = 12 \\ x = 12 \div 4 \\ x =3 \\ \\ x + y = 3 + 4 = 7[/tex]

Ответ: 7