According to data from the American Hospital Association, the rate of change in the number of hospital outpatient visits, in millions, in the United States each year from 1980 to the present can be approximated by ƒ′(t) = 0.001483t(t - 1980)^0.75, where t is the year.

(a) Using the fact that in 1980 there were 262,951,000 outpatient visits, find a formula giving the approximate number of outpatient visits as a function of time.
(b) Use the answer to part (a) to estimate the number of outpatient visits in the year 2020.