Solve.The sales of typewriters have declined considerably in recent years because of the advent of computers. Assume that there were 21 million typewriters sold in 1980 and 5 million sold in 1990. In addition, assume the sales are decreasing according to the exponential decay model. Find the value k, and write an exponential function that describes the number of typewriters sold after time t, in years. (Round decimals to three places.)
A. k = 0.161; S(t) = 21e-0.161t, where S(t) is in millions and t is the number of years since 1980.
B. k = 0.304; S(t) = 21e-0.304t, where S(t) is in millions and t is the number of years since 1980.
C. k = -0.144; S(t) = 21e-0.144t, where S(t) is in millions and t is the number of years since 1980.
D. k = 0.144; S(t) = 21e-0.144t, where S(t) is in millions and t is the number of years since 1980.
Answer: D
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