Total personal income with U.S. Department of Commerce data for selected years from 1960 and projected to 2018, the rate of change of U.S. total personal income can be modeled by
dl/dt = 12.59t-51.74
billions of current dollars per year, where t = 0 represents 1960.
(a) If U.S. total personal income was $8429.7 billion in 2000, find the function that models I(t).
(b) What does I(t) predict for the U.S. total personal income in 2015?