For these types of algebra problems, you're trying to get whatever they tell you by itself on one side of the equals sign, meaning that you have to move everything else over by adding/subtracting or whatever else.
In this problem you have to get s by itself. All you do is just subtract 4r from both sides to get:
-2 - 4r = s
Because there are 2 variables/unknowns (s and r) you have no way of actually solving this problem without having a 2nd equation or something. So thats all you can do