Given that opulation of 100,000 decreases by 2% each year.
Now question says to write a function in terms of t that represents the situation.
Question is talking about population decrease so we can apply decay formula. which is given by:

Where A is the population at any time t.
is the initial population so 
r is the rate of decrease so r=2%=0.02
t is the number of years
Now plug those values, we get:


Hence required function is
.