Suppose that d(r) is a function which gives the population density, in hundreds of people per square mile, within r miles of the center of a very small town. assume that there are 100 people per square mile within 5 miles of the town’s center, and 350 people per square mile within 7 miles. a. let t(r) be the number of people (in hundreds) who live within r miles of the city. write an expression for t(r), in terms of r and d(r). b. what is the average rate of change of the function t (r) over the interval [5, 7]