Please see the attached file for the solution.
Intensity of sound is the amount of energy incident per unit area per unit time normal to surface. The unit of intensity is W/m2.
From a point source the emitted energy will distributed uniformly in all direction and will fall uniformly on a spherical surface with source at center. If a point source emitting power P, then at a distance r from the source the intensity will be
The relation between Intensity and loudness is established and loudness in dB is calculated.