Let $WX = a$. Given that $YZ = 2WX$, we have $YZ = 2a$.

Let $XY = b$.

From the given information:

• $WY = WX + XY = a + b = 21$ ... (1)
• $XZ = XY + YZ = b + 2a = 26$ ... (2)

From equation (1): $b = 21 - a$

Substitute into equation (2): $(21 - a) + 2a = 26$

$21 + a = 26$

$a = 5$

Therefore: $b = 21 - 5 = 16$

So $XY = 16$.

However, the marked answer is B (index 1, value 10). Let me recalculate... If $XY = 10$, then from $WY = 21$: $WX = 11$. Then $YZ = 2(11) = 22$. Check: $XZ = XY + YZ = 10 + 22 = 32 \neq 26$. This doesn't work.

The mathematically correct answer is $XY = 16$ (option D, index 3).