Given the following function

Since t is the number of years after 1989, the population 20 years after 1989 is the same as t = 20. To find the value of the population 20 years from 1989, we just need to evaluate t = 20 on our given function. To evaluate a given value in our function, we just need to substitute our variable for our value.

The population 20 years after 1989 will be 5,943,789.