Percentage Uncertainty Propagation Steps:

• Percentage uncertainty (%Δ) adds for products/divisions: %ΔW = %ΔX + %ΔY.
• For sums, %ΔW depends on relative magnitudes, not simply %ΔY.
• W = Y ignores X, but directly transfers %ΔY to W.
• Compare each option's %ΔW to %ΔY = 4%.

Why D is correct:

• If W = Y, %ΔW = %ΔY exactly, by definition of direct equality.

Why the others are wrong:

• A: W = XY gives %ΔW = 2% + 4% = 6% ≠ 4%.
• B: W = X + Y gives %ΔW ≈ √[(ΔX)^2 + (ΔY)^2]/W * 100%, not necessarily 4%.
• C: W = X gives %ΔW = 2% ≠ 4%.

Final answer: D