This does not appear to make sense, could you perhaps add signs such as multiplication, division, etc.
A square, isosceles triangle or parallelogram
You can solve the equation for y:
y = (12 - 4x)/-3 = (4/3)x - 4
And for x:
x = (12 + 3y)/4 = (3/4)y + 3
Now for ...
x=0, y = (4/3)·0 -4 =
-4 y=0, x = (3/4)·0 +3 =
3 x=9, y = (4/3)·9 -4 = 12-4 =
8 y=-8, x = (3/4)·(-8) +3 = -6 +3 =
-3