(a) If the dB are sound-intensity dB (dB-SIL), then the reference level is I0 = 10^-12 W/m² 130 = 10*log(I/I0) = 10*[log(I) + 12] 13 = log(I) + 12 log(I) = 1, I = 10 W/m² This is covering an area of 4*π*(1.3²), so the total power is 10*4*π*(1.3²) W. 212.4 W (b) 85 dB = 10*[log(I) + 12] log(I) = -3.5I = 10^-3.5 W/m² The distance is such that the area covered by 985 W yields 10^-3 W/m²: 212.4/(4*π*r²) = 10^-3.5r = √[212.4*10^3.5/(4*π)] r = 231.2 m

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