So the easiest method that can be used would be substitution. This is what you do...
Plug in the y-value into the second equation.
-4x + 3(x - 4) = -3
Distribute.
-4x + 3x - 12 = -3
Combine like-terms.
-1x - 12 = -3
Add 12 to both sides to isolate the variable.
-1x = 9
Divide.
x = -9
Now we need to find the y-value.
Plug in x with -9 in the first equation.
y = x - 4
y = -9 - 4
y = -13
So your solution is (-9, -13)
I hope this helps love! :)