Choice C is the correct answer. We use substitution since $y = 2x + 5$ is already isolated.

Step 1: Substitute $y = 2x + 5$ into $3x - y = 1$: $3x - (2x + 5) = 1$$3x - 2x - 5 = 1$$x - 5 = 1$$x = 6$

Step 2: Find $y$ using $y = 2x + 5$: $y = 2(6) + 5 = 12 + 5 = 17$

Solution: $(6, 17)$

Verification: $3(6) - 17 = 18 - 17 = 1$ ✓

💡 Strategic Tip: When one equation is solved for y, substitute into the other equation.

Choice A is incorrect because$3(8) - 21 = 24 - 21 = 3 \ eq 1$.

Choice B is incorrect because$3(4) - 13 = 12 - 13 = -1 \ eq 1$.

Choice D is incorrect because$3(5) - 15 = 15 - 15 = 0 \ eq 1$.