At 25 m, L = 80dB = 10 log(I/I0)

I/I0 = 108

I = 108 I0= I1

(I1/I2)=(r1/r2)2

I2 = I1(r1/r2)2 = (I0108)(25/50)2 = I0108/4

Therefore at 50 m, L = 10 log[(1/4)I0108/I0] = 10 log 108 - 10 log 4 = 80 - 6 = 74 dB

Answer is E

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