Answer
Option D is correct.
x = 6
Explanation
9 : x = x : 4
To solve this, we know that ratios can be written in fraction form
(9/x) = (x/4)
[tex]\begin{gathered} \frac{9}{x}=\frac{x}{4} \\ \text{Cross multiply} \\ x^2=9\times4 \\ x^2=36 \end{gathered}[/tex]Take the square root of both sides
√(x²) = √(36)
x = 6
Hope this Helps!!!