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 = 50). Year 1940 1950
1960
1970 1980 1990
E 6.9 9.4 13.0 18.5 20.9 19.6
Estimate the amount of nitrogen oxides emitted from 1940 to 1990 using five subintervals and:
a. a left Riemann sum al b. a right Riemann sum. C. a trapezoidal approximation