Using data from 2010 and projected to 2016, the fraction of U.S. cell phone users who are smart phone users can be modeled by the function

where t is equal to the number of years after 2010
(a) Is the function continuous for years from 2010 onward?
(b) Evaluate limt†’ˆž f (t) if it exists to find a horizontal asymptote.
(c) When can we be sure this model is no longer valid for this application?
(d) Does the limt†’ˆž f (t) give the long-term projection of the fraction of smart phone users?

21.35t + 69.59 4.590t + 233.1 f(t) =