Physics: Sound and Decibels

I have a physics question if anybody can help me out.

At 1m away a politiction produces a sound intensity at 80 dB in a park without obstables.

Approx what is the sound intensity at 30 meters away? I'm considering using 1 over R formula,

however it doesn't give an answer in dB.

Sound I be using logarithms?

Formula:

$\begin{array}{|rrcll|} \hline Let & I_1 &=& 80\ dB \\ Let & r_1 &=& 1\ m \\ Let & I_2 &=& ? \\ Let & r_2 &=& 30\ m \\\\ & I_2 &=& I_1 - 10 \cdot |~ \log( (\frac{d_1}{d_2})^2 ) ~| \qquad \text{ sound intensity }\\\\ & I_2 &=& 80\ dB - 10 \cdot |~\log( (\frac{1\ m}{30\ m})^2 )~| \\ & I_2 &=& 80\ dB - 10 \cdot |~\log( 0.00111111111 )~| \\ & I_2 &=& 80\ dB - 10 \cdot |~(-2.95424250944)~| \\ & I_2 &=& 80\ dB - 10 \cdot 2.95424250944 \\ & I_2 &=& 80\ dB - 29.5424250944 \\\\ & \mathbf{ I_2 } & \mathbf{ = } & \mathbf{ 50.4575749056\ dB } \\ \hline \end{array}$