Let f(x) = 0.8x^3 + 1.9x^2- 2.7x + 23 represent the number of people in a country where x is the number of years after 1998 and f(x) represent the number of people in thousands. Include units in your answer where appropriate. (round to the nearest tenth if necessary)

a) How many people were there in the year 1998?

b) Find f(15)

c) x = 15 represents the year

d) Write a complete sentence interpreting f(19) in context to the problem.