[(?)2 + (18)2] ÷ 125 = 3.56

Answer: Option A

Let, $$\frac{x^2+{\left(18\right)}^2}{125}=3.56$$
Then,
$$\begin{array}{rl}& x^2+324=125\times 3.56=445\\ & \Rightarrow x^2=121\\ & \Rightarrow x=11\end{array}$$