Choice C is the correct answer. We use substitution since $y = 4x$ is already isolated.

Step 1: Substitute $y = 4x$ into $2x + y = 30$: $2x + (4x) = 30$$6x = 30$$x = 5$

Step 2: Find $y$ using $y = 4x$: $y = 4(5) = 20$

Solution: $(5, 20)$

Verification: $2(5) + 20 = 10 + 20 = 30$ ✓

💡 Strategic Tip: Substitution works best when one equation is already solved for a variable.

Choice A is incorrect because$2(6) + 24 = 12 + 24 = 36 \ eq 30$.

Choice B is incorrect because$2(4) + 16 = 8 + 16 = 24 \ eq 30$.

Choice D is incorrect because$2(3) + 12 = 6 + 12 = 18 \ eq 30$.