The total amount of spending per year, in billions of dollars, on pets in the United States

Question:

The total amount of spending per year, in billions of dollars, on pets in the United States x years after 2000 is given by the function
P(x) = 2.1782x + 25.3
(Source: Animal Pet Products Manufacturing Association)
a) Determine the total amount of spending per year on pets in 2005 and in 2010.
b) Find P-1(x) and explain what it represents.