A + (a-2) = (a+s) - (a+3) ?

Simplify

2a - 2 = s + 3

Add two to each side

2a = s + 5

And that's all you can do with it ...

But pretending that you made an error and that s is meant to be a, because they're right next to each other (You might have even commented it, I can't see comments from phone) then

2a = a + 5

Subtract a from each side

a = 5

Which seems more logical