Answer:
2
Step-by-step explanation:
All the triangles are similar, so ...
... 4/y - y/9
... 36 = y² . . . . . multiply by 9y
... 6 = y
From the Pythagorean theorem, ...
... x² = 4² + y² = 4² + 6²
... x² = 52 = 4·13
... x = √(4·13) = 2√13
Green Box: 2
