A source of sound operates at 2.0 kHz and 20 W , radiating sound...

The intensity of sound at a distance $r$ from a point source radiating uniformly in all directions is given by the power divided by the surface area of a sphere of radius $r$.

$I = \dfrac{P}{4 \pi r^2}$

Given:
Power of the source, $P = 20 \text{ W}$
Distance, $r = 6.0 \text{ m}$

Substituting the values into the formula:

$I = \dfrac{20}{4 \pi (6.0)^2}$

$I = \dfrac{20}{4 \pi \times 36}$

$I = \dfrac{5}{36 \pi} \text{ W m}^{-2}$

Using $\pi \approx 3.14$:

$I \approx \dfrac{5}{113.04} \text{ W m}^{-2}$

$I \approx 0.0442 \text{ W m}^{-2}$

$I \approx 44 \text{ mW m}^{-2}$

The frequency, speed of sound, and density of air are extra information not required for this calculation.