Answer
$L(I)=90$ dB
Work Step by Step
$I=10^{-3}$ watts per square meter
Putting in the equation:
$L(I)=10\log \frac{10^{-3}}{10^{-12}}$
$L(I)=10\log (10^{-3}\times 10^{12})$
$L(I)=10\log10^9$
$L(I)=10\times 9\log10$
$L(I)=90\log10$
$L(I)=90$ dB