A water sample initially contains 500 ppm of pollutant C, which decays continuously at rate 0.08 h−1. Simultaneously, pollutant D is introduced at an initial concentration of 50 ppm and increases continuously at rate 0.05 h−1. Which of the following best describes when the two concentrations are equal and which pollutant has the greater concentration two hours afterward?
a) They are equal at approximately 10.6 h; thereafter pollutant D has the greater concentration.
b) They are equal at approximately 17.7 h; thereafter pollutant D has the greater concentration.
c) They are equal at approximately 17.7 h; thereafter pollutant C has the greater concentration.
d) They are equal at approximately 7.7 h; thereafter pollutant D has the greater concentration.