Choice D is the correct answer. The $y$ terms are opposites ($+y$ and $-y$), so we can add the equations to eliminate $y$.

Step 1: Add the two equations: $(4x + y) + (4x - y) = 18 + 10$$8x = 28$$x = \frac{28}{8} = \frac{7}{2} = 3.5$

Step 2: Substitute $x = 3.5$ into the first equation: $4(3.5) + y = 18$$14 + y = 18$$y = 4$

Solution: $(3.5, 4)$

Verification: $4(3.5) - 4 = 14 - 4 = 10$ ✓

💡 Strategic Tip: Opposite coefficients make elimination by addition very efficient.

Choice A is incorrect because$4(6) + (-6) = 24 - 6 = 18$ ✓, but $4(6) - (-6) = 24 + 6 = 30 \ eq 10$.

Choice B is incorrect because$4(4) + 2 = 16 + 2 = 18$ ✓, but $4(4) - 2 = 16 - 2 = 14 \ eq 10$.

Choice C is incorrect because$4(5) - (-2) = 20 + 2 = 22 \ eq 10$.