Chapter 6 - Logarithmic Functions - 6.6 Solving Logarithmic Equations - 6.6 Exercises - Page 534: 15

$I=10^4=10,000$ cm

$M=8$ $S=10^{-4}$cm Putting in the formula $M=\log\frac{I}{S}$ and solve for $I$: $8=\log \frac{I}{10^{-4}}$ $8=\log( 10^4I )$ $8=\log( 10^4I )$ $10^4I=10^8$ $I=\frac{10^8}{10^4}$ $I=10^{8-4}=10^4=10,000$