\begin{aligned} \sqrt{\frac{0.081 * 0.484 }{0.0064 * 6.25}} \end{aligned}

Answer: Option D

Explanation:

L.C.M. of 21, 36, 66 = 2772

Now, 2772 = 2 x 2 x 3 x 3 x 7 x 11

To make it a perfect square, it must be multiplied by 7 x 11.

So, required number = 2 x 2 x 3 x 3 x 7 x 7 x 11 x 11 = 213444

Answer: Option C

Explanation:

\begin{aligned}
= \sqrt{248+\sqrt{64}}
\end{aligned}

\begin{aligned}
= \sqrt{248+8}
\end{aligned}

\begin{aligned}
= \sqrt{256}
\end{aligned}

\begin{aligned}
= 16
\end{aligned}

Answer: Option C

Explanation:

21*21*21 = 9261

Answer: Option A

Answer: Option C