-7 - 12 = - 7х + 3(-4 - x)

x = -1.8

Step-by-step explanation:

-7 - 12 = -7x + 3 (-4 - x)

-7x + 3 (-4 - x) = -7 - 12

P.S I switched the order cuz I find it easier to solve this way.

-7x + 3 (-4 - x) = -7 - 12

Distribute

-7x - 12 - 3x = - 7 + 13

Add 12 to both sides

-7x - 3x = -7 + 13 + 12

Combine like terms

-10x = 18

Divide both sides by -10

x = -1.8

thats not a system of equations, that is a solution