Circle City, a typical metropolis, is densely populated near its center, and its population gradually thins out toward the city limits. In fact, its population density is 10,000(5 - r) people/square mile at distance r miles from the center. (a) Assuming that the population density at the city limits is zero, find the radius of the city. The radius of the city is 5 miles. (b) What is the total population of the city? Round your answer to the nearest integer. The total population of the city is