1. **Problem:** Solve the system using substitution: $$\begin{cases} y = -x + 4 \\ y = 3x \end{cases}$$ 2. **Formula and rules:** Substitution means replacing one variable with an expression from the other equation. 3. **Step 1:** Since both equal $y$, set them equal: $$-x + 4 = 3x$$ 4. **Step 2:** Solve for $x$: $$-x + 4 = 3x$$ $$4 = 3x + x$$ $$4 = 4x$$ $$x = \frac{4}{4}$$ $$x = 1$$ 5. **Step 3:** Substitute $x=1$ into $y = 3x$: $$y = 3(1) = 3$$ 6. **Answer:** $$\boxed{(x,y) = (1,3)}$$ This is the solution to the first system. q_count is 11 because 11 distinct problems were given.