Answer
a. 5.858
b. 63.09 cm
Work Step by Step
Given the magnitude equation $M = \log \frac{I}{S}$
with $S = 10^{-4}$
a. Solve for M given $I = 72.1 cm$
$M = \log \frac{72.1}{10^{-4}}$
$M = \log 72.1 + \log 10^{4} = 5.858$
b. Given M = 5.8, find the intensity
$5.8 = \log \frac{I}{10^{-4}}$
$10^{5.8} = \frac{I}{10^{-4}}$
$I = 10^{1.8} = 63.09 cm$
