The answer would be x = -0.4
You first have to move the 0.4 to the other side of the equation by subtracting it:
-9x + 0.4 = 4
-0.4 -0.4
Leaving the -9x by itself and the 4 now becomes 3.6:
-9x = 3.6
Next you have to divide by -9 on both sides to get x by itself:
-9x = 3.6
— —
-9 -9
Leaving you with x = -0.4
