Answer:
(a) 8√3
Explanation:
All of the triangles are similar, so the ratio of hypotenuse to long side is the same for all. Comparing the middle-size triangle to the largest, we have ...
... x/12 = 16/x
... x² = 192 . . . . . . . . . . . . . multiply by 12x; next take the square root
... x = √192 = 8√3 . . . . . . seems to match answer choice (a)