In order to determine the boa constrictor population after 2, 3 and 4 years, use the values of the function on the graph (which is the boa polpulation), for the values of time = 2, 3 and 4.
You can notice that for time t = 2, the value of the function is 20.
For t = 3, you have that the function has the value of 40.
For t = 4, the function has a value of 80.
Hence, you have:
after 2 years the boa population is 20
after 3 years the boa population is 40
after 4 yearsthe boa population is 80