#### Answer

4.7

#### Work Step by Step

We are given that the formula $R=log(\frac{a}{T})+B$ can be used to find the intensity R of an earthquake on the Richter scale (where a is the amplitude in micrometers, T is the time in seconds between waves, and B is a constant).
In this case, $a= 450$, $T=4.2$, and $B=2.7$.
We can plug in these values to find R. Recall that $log(\frac{a}{T})$ is written in the form of the common logarithm and has a base of 10.
$R=log(\frac{450}{4.2})+2.7=log(107.14)+2.7=2+2.7=4.7$