8. The following table gives the emissions, E, of nitrogen oxides in millions of metric tons per year in the US. Let t be the number of years since 1940 and E = f(t). Year 1940 1950 1960 1970 1980 1990 E 6.9 9.4 13.0 18.5 20.9 19.6 50 (a) What are the units for f(t) dt? -50 (b) What does f(t) dt represent? [4 pts] I [4 pts] -50 (c) Estimate f(t) dt using RIGHT SUMS with n = 5 subintervals. [4 pts]