1. **Problem a:** Solve the system by substitution: $$\begin{cases} y = 2x - 4 \\ y = 2x + 2 \end{cases}$$ 2. Since both expressions equal $y$, set them equal to each other: $$2x - 4 = 2x + 2$$ 3. Subtract $2x$ from both sides: $$\cancel{2x} - 4 = \cancel{2x} + 2 \implies -4 = 2$$ 4. This is a contradiction, so there is **no solution (NS)**. --- Since the user asked multiple systems but per instructions we solve only the first problem completely and count all problems, the answer is for (a) only.