Advanced functions - inequalities?

Question

The number of skunks in an area can be modelled by the function n(t) = -t^3-2t^2+21t, where t is the number of weeks since July 1st and n, is the number of skunks, in hundreds.  

1) When will the skunk population be greater than 1800? 

2) what happens to the population 6 weeks after July 1st? 

- I’m just really confused by this question, and I’m unsure of how to go about answering it using inequalities...

Answer 1

1) -t^3 -2*t^2 + 21t - 18 = 0

t^3 +2*t^2 - 21t + 18 = 0

t=1 or t=3, so before week 1 and after week 3

2) -6^3 - 2*6^2 + 21*6 = -36 < 0 so the skunks are extinct