[tex]A = \Big\{x\in \mathbb_{N} \Big| $ \ $4\ \textless \ 2x-4\leq 8}\Big\}\\ \\ \\ 4\ \textless \ 2x-4\leq 8\Big|+4 \Rightarrow 8 \ \textless \ 2x\leq 12 \Big|:2 \Rightarrow 4\ \textless \ x\leq 6 \\ \\ \Rightarrow x \in (4,6] \Rightarrow A = \Big\{5,6\Big\} \\ \\ S = 5+6 \Rightarrow \boxed{S = 11}[/tex]
