How Do You Calculate Decibel Intensity at a Distance in Spherical Waves?

[PCPanos]

Homework Statement

The intensity of a certain spherical wave is 8.0 W/m^2 at a distance of 1.0 m from the source. If the medium is isotropic and nonabsorbing, calculate the decibel intensity 100m from the source.

Homework Equations

β=10ln(I1/I0)

The Attempt at a Solution

I know how to use these equations... And to find the original dB level i use
β=(10dB)ln(8.0/10^-12)

Im just not sure what to do to find intensity 100m away?

 

[mfb]

What do you mean with "original dB level"?

How does intensity depend on distance for spherical waves without absorption?

 

[haruspex]

"Decibel" is very confusing because the term is used both for relative and absolute intensities. As far as I am aware, the unit dB always denotes (or should always denote) a relative intensity. If an absolute intensity is intended then it should be qualified to indicate the reference level, like dBm or dBmW.
Where does your 10^-12 come from?