12) Given the following equation

$$
4=\sqrt{7+\sqrt{9+\sqrt{4+x}}}
$$

what is the value of $x$?
(A) 36
(B) 46
(C) 56
(D) 68
(E) 5180
12) The answer is ( $\mathrm{E})$

By repeatedly squaring, we obtain:

$$
\begin{gathered}
16=7+\sqrt{9+\sqrt{4+x}} \\
81=9+\sqrt{4+x} \\
5184=4+x
\end{gathered}
$$

from which $x=5180$. The solution is certainly acceptable because we have always squared positive quantities.