So, let's first focus on the first year:
the population then would be: 23000* (100+2)%
100% is the old population the 2% is the incease, so in total it's 102%, or 1.02 - the same number written differently.
So it will be 23000*1.02
After two years it will be 23000*1.02*1.02, and so on
so after x years it will be:
y=23000*[tex]1.02^{z} [/tex]