Question

Помогите плииииииииииииз

Answer 1

$4x - ay = 7 \: \: \: | \times 3 \\ 12x + 18y = 21 \\ \\ 12x - ay = 21 \\ 12x + 18y = 21 \\ \\ - a = 18 \\ a = - 18$

Ответ: а = - 18