急 ! Logarithmic Function EX3

general form for seismology: Magnitude = log [Amplitude] + C where C is a constant

28a.
8.1 - 7.5 = log [A19/9] - log [A21/9]
0.6 = log [A19/9 / A21/9]
10^0.6 = [A19/9 / A21/9]
A19/9 / A21/9 = 3.98

28b.
8.1 - 7.0 = log [A19/9] - log [A30/4]
1.1 = log [A19/9 / A30/4]
10^1.1 = [A19/9 / A30/4]
A19/9 / A30/4 = 12.6

general form for soundness: dB = 10log [Intensity] + C where C is a constant
29.
let x be the intensity level of car
122 - x = {10 log [Iair] + C} - {10 log [Icar] + C}
122 - x = 10 log [Iair] - 10 log [Icar]
122 - x = 10 log [Iair/ Icar]
122 - x = 10 log [10000]
122 - x = 40
x = 82