The function p(t)=21000+1800t computes the population of a city from years 1980-2001, with t=0 representing 1980. what is the domain and range in correct interval notation?

In year 2001, the corresponding value of t is 2001 - 1980 = 21. Thus the
  domain is [0, 21]

The values of p(t) increase monotonically between those values of t, so the range of p(t) is p(0) = 21,000 to p(21) = 58,800.
  range is [21000, 58800]