The value of 40 + 9 81 is = ?

Answer: Option C

$$\begin{array}{rl}& \sqrt{40+\sqrt{9\sqrt{81}}}\\ & \Rightarrow \sqrt{40+\sqrt{9\times 9}}\\ & \Rightarrow \sqrt{40+9}\\ & \Rightarrow \sqrt{49}\\ & \Rightarrow 7\end{array}$$