Question

The population of a certain animal species you are studying decreases at a rate of 3.5% per year. Only 80 of the animals in the habitat remain after 3 years of conducting your research. What was the initial amount of animals

Answer 1

The function:
f ( x ) = x * 0.965^t
where x is the initial amount and t is the number of the years
80 = x * 0.965^3
80 = x  *  0.89632
x = 80 : 0.89632 ≈ 89
Answer:
The initial amount of animals was 89.

Hope this helps :)