I'm not sure what this diagram is meant to show, but if you want to solve the equation 18 - 4x = -2, then you could follow these steps.
18 - 4x = -2
18 - 4x - 18 = -2 - 18 ... subtract 18 from both sides
-4x = -20
-4x/(-4) = -20/(-4) ... divide both sides by -4
x = 5 is the solution to the equation
As a check, let's plug it in
18 - 4x = -2
18 - 4(5) = -2
18 - 20 = -2
-2 = -2 ... solution is confirmed