A heavy industrial plant located in the center of a small town emits particulate matter into the atmosphere Suppose that the concentration of particulate matter in parts per million at a point d miles from the plant is given by C 220 15d2 If the boundaries of the town form a rectangle 6 miles long and 10 miles wide what is the average concentration of particulate matter throughout the city Express C as a function of x and y set up a double integral and evaluate it The average concentration of particulate matter is parts per million