Question 52969
There is more than one way to do this.  I don't have your book, so I'm just going to show you the easiest way I can think of.
100(new-original)/original=rate change in percentage:
Original=12000
New=10920
{{{100(10920-12000)/12000}}}
{{{100(-1080)/12000}}}
{{{-108000/12000}}}
-9%
The negative sign tells you that it is a rate decrease.  Therefore the rate of decrease is 9%.