77.
26 dB; 18 dB; 12 dB; 6 dB
200 ft
a=10(4+log 4)≈46; b=−20
r=20010L/20
79. 5×1015 vs 2.5×1016; earthquake is 5 times more powerful.
81. [875, 885] Hz
83. −2.2
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