Using Social Security Administration data for selected years from 2012 and projected to 2050, with a purchasing

Question:

Using Social Security Administration data for selected years from 2012 and projected to 2050, with a purchasing power of $1.00 in 2012, the function
P(x) = 1.078(1.028-x)
gives the purchasing power of a 2012 dollar as a function of x, the number of years past 2010.
(a) Find and interpret P(18).
(b) Solve algebraically to find the year when the purchasing power of a 2012 dollar is expected to reach $0.48.