Choice C is the correct answer. Since $x = 5y$ is already isolated, we can directly substitute it into the second equation.

Step 1: Substitute $x = 5y$ into $2x + y = 33$: $2(5y) + y = 33$$10y + y = 33$$11y = 33$$y = 3$

Step 2: Find $x$ using $x = 5y$: $x = 5(3) = 15$

Solution: $(15, 3)$

Verification: $2(15) + 3 = 30 + 3 = 33$ ✓

💡 Strategic Tip: When a variable is already isolated, substitution is the most efficient method.

Choice A is incorrect because$2(10) + 2 = 20 + 2 = 22 \ eq 33$.

Choice B is incorrect because$2(20) + 4 = 40 + 4 = 44 \ eq 33$.

Choice D is incorrect because$2(25) + 5 = 50 + 5 = 55 \ eq 33$.