Answer:
First we need to calculate the height of the triangle ( because from that, we can also calculate both x and y)
We know that: h² = b'c'
And in our case:
b' = 9
c' = 3
=> h² = b'c' = 9 · 3
=> h = √(9 · 3) = √27
Now using pythagorean theorem:
(√27)² + 3² = x²
=> x² = 27 + 9
=> x = √(27 + 9) = √36 = 6
So x = 6 and the answer is C.