Answer
The required value is $120\text{ decibels}$
Work Step by Step
According to the given information in the question,
$D=10\log \left( \frac{I}{{{I}_{o}}} \right)$
And
$I={{10}^{12}}{{I}_{o}}$
Plug in the value:
$D=10\log \left( \frac{{{10}^{12}}{{I}_{o}}}{{{I}_{o}}} \right)$
Use $\log \left( {{a}^{b}} \right)=b\log \left( a \right)$ to obtain:
$\begin{align}
& D=10\cdot 12\log \left( 10 \right) \\
& D=120
\end{align}$
