What is power attenuation rate for a walking away person from the sound source?

We know using the formula NdB = 10 log10 (P2/P1) formula proves that -3dB gives us half the power of the input source.

By using the Inverse square law I2/I1 = [d1/d2]2  you can calculate the Intensity in decibels in relation to distance.

For example, if the SPL at I1  is 20dB at a distance of 5 meters (d1), then the intensity of I2 , at a distance of 10 meters from I1  would be 14 dB. This means that the sound would have attenuated by 6dB in a total distance of 15 meteres.