(a) Use the fact that the population was 250 million in 1990 (t = 0) to formulate a logistic model for the US population. (Assume the carrying capacity is 4250 million. Assume P is the population in millions, k is the relative growth rate, and t is the time in years since 1990.) P(t) = (b) Determine the value of k in your model by using the fact that the population in 2000 was 275 million. (Round your answer to eight decimal places.) k= (c) Use your model to predict the US population in the years 2100 and 2200. (Round your answers to the nearest person.) year 2100 P = million year 2200 P= million (d) Use your model to predict the year in which the US population will exceed 350 million