Pollutants in a factory are removed by air filters that become less efficient as time goes on. The following measurements, made twice each month, show the rate at which pollutants are removed Time, t (months) 0 0.5 1 1.5 2 2.5 3 Rate of removal, r (tons/month) 6.0 4.0 2.8 2.0 1.4 1.0 |0.7 a. Find an upper estimate of the total amount of pollutant that is removed in the three month period. b. Find a lower estimate of the total amount of pollutant that is removed in the three month period C. Give a left estimate of fr(t) dt with At = 1. d. Give a right estimate of fir(t) dt