I am stuck on this question for my homework I know that it is giving me all the info but I feel like it is a puzzle and I am missing a piece the question is:
The federal debt D in trillions of dollars
held by foreign and international investors x
years after 1970 can be modeled by
D(x) =1/320(x^2)-3/80(x) where 15<x<40
where 15 … x … 40.
(a) Evaluate D(40) and interpret the result.
(b) Determine the year when the federal debt held
by foreign and international investors first
reached $500 billion ($0.5 trillion).
Thank You in Advance for you help.