Use logarithms to solve the equation 2^(n-3) = 18000, giving your answer correct to 3 significant figures.

To find the answer first you have to take a log of both sides.

I am going to use log to the base 2 for my example - but any base will work as long as they are the same on both sides of the equals sign 

log(2^n-3)=log(18000)

Using the rules of logerithms you can bring down the power

(n-3)log(2)=log(18000)

As I am using base 2 log(2)=1

n-3=log(18000)

n=log(18000)+3

n=17.1