Answer
$I=7943.28$ cm
Work Step by Step
$M=7.9$
$S=10^{-4}$
Putting in the equation:
$M=\log\frac{I}{S}$
and solving for $I$:
$7.9=\log \frac{I}{10^{-4}}$
$\log (10^4 I)=7.9$
$10^4I= 10^{7.9}$
$I=\frac{10^{7.9}}{10^4}=10^{3.9}\approx 7943.28$ cm
