According to data from the Bureau of Transportation Statistics, the rate of change in the number of local transit vehicles (buses, light rail, etc.), in thousands, in the United States from 1970 to the present can be approximated by ƒ′(t) = 4.0674 * 10^-4t(t - 1970)^0.3, where t is the year. 

(a) Using the fact that there were 61,298 such vehicles in 1970, find a formula giving the approximate number of local transit vehicles as a function of time.
(b) Use the answer to part (a) to estimate the number of local transit vehicles in the year 2020.