3. A city is shaped roughly like a rectangle 20 miles long and 10 miles wide. The population density of the city at a distance r miles from one of the sides of length 20 miles is given by 2000 1+ 72 People/mi-. (a) Sketch a picture of the city that includes the dimensions, a representative slice, and the variable r clearly defined. (b) Determine the population of a representative slice. Population of a Slice: Supporting Work (required to get full credit): (c) Write an integral which represents the total population of the city. You do not need to evaluate the integral. Integral Representing the Total Population: Supporting Work