Ecologists estimate that, when the population of a certain city is x thousand persons, the average level l of carbon monoxide in the air above the city will be l ppm (parts per million), where upper l 80 + 0.4 x + 0.0006 x squared. the population of the city is estimated to be x 752 + 23 t + 0.5 t squared thousand persons t years from the present. find the rate of change of carbon monoxide with respect to the population of the city, and the time rate of change of the population when t2. how fast (with respect to time) is the carbon monoxide level changing at time t2?