Let C(t) be the total value of US currency (coins and banknotes) in circulation at time t, where tis measured in years and t = 0 in the year 1980. The table gives values of this function from 1980 to 2000, as of September 30, in billions of dollars. ear 1980 1985 1990 1995 2000 CW 129.9 198.9 275.9 10.3 568.6 Using the exponential model and the values of C(t)in 1980 and 1985, estimate C'(t) in 1990. Answers are in billions of dollars per year. Round your answer to two decimal places. 0 a) 16.92 0 b) 44.45 0 c) 137.45 0 d) 27.43 0 e) 23.51