find the formula

A population has size 8000 at time http://edugen.wiley.com/edugen/share...=1221687554198 with http://edugen.wiley.com/edugen/share...=1221687554198 in years. (a) If the population decreases by 100 people per year, find a formula for the population, http://edugen.wiley.com/edugen/share...=1221687554198 at time http://edugen.wiley.com/edugen/share...=1221687554198
(b) If the population decreases by 15% per year, find a formula for the population, http://edugen.wiley.com/edugen/share...=1221687554198 at time http://edugen.wiley.com/edugen/share...=1221687554198

(a) I think it is 8000(-1.0100)^x

PLEASE HELP ME!!!!!!!!!!!

You can check that your formula is right by substituting some obvious values for x.
So after 1 year the population should be 7900 as it has decreased by 100 people in that year. Your formula gives -8080.

The right answer to a is 8000-100x,
and b is .

I don't like just giving people answers but I don't really know a process to get these; I just know them. sorry.