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The table below gives U.S. lead emissions, $L$ , into the environment in millions of metric tons for 1970-1992. Let $t = 0$ in 1970.

Year	1970	1975	1980	1985	1988	1989	1990	1991	1992
Lead emissions	264.1	121.8	42.2	14.9	9.1	7.1	6	4.8	4.2

(a) Find an exponential model for these data.

Lead emission, $L(t) =$ .

(b) Find a fourth-degree polynomial model for these data.

Lead emission, $L(t) =$ .

(c) Which of these curves gives a better model for the data?

A. exponential model
B. fourth-degree polynomial

(d) Estimate the lead emission in 1981 according to the polynomial model in part (b).

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