Beat frequency, find intensity at distance from sources?

[Inertigratus]

Homework Statement

Three sources are emitting sound at 0.8W, one at 200 Hz, second one at 201 Hz and third one at 202 Hz.
The sound travels in a shape of a half sphere.
Find the intensity at 3m distance from the source
(the sources are said to be very close to each other so I guess they can be thought of as one "source")

Homework Equations

f_beat=|f₁- f₂|
I = W / At
I = p₀² / 2Z

The Attempt at a Solution

Not really sure how to proceed, I can't seem to find the right equations.
I had some trouble understanding the problem. Now I understand that the three sources produce a beat frequency (I think?) and then you have to use that to find the intensity.

Any ideas?

 

[Inertigratus]

Anyone?
A quick answer would be appreciated, all I need is to know which formulas to use.

I was thinking about the sound pressure amplitude formula, but that requires me to know the wave amplitude. The formula power over area won't work either as it isn't depending on the frequencies. I can't really come up with any formulas...

About the shape, I think they are placed like a triangle with the three sources on the corners and with minimal distance between them. The "half-sphere" is in the direction of the wave and I think that each source has it's own "half-sphere".

The three sources make up a siren, but I don't think the problem has anything to do with the doppler effect.

 

[Inertigratus]

The pressure amplitude formula:
p0 = 2*pi*s0 / k*lambda

Here k is a constant and lambda (wavelength) can be replaced by v/f, (phase velocity/frequency)
Still as I said, s0 (wave amplitude) is missing (?) and the area/radius doesn't have a place in the formula.
...
Any help?