A nature conservation organization tracks the population of an endangered species of foxes over time. The population number is modeled by the function (x)=−1.20.7x+10,000(x)=−1.20.7x+10, 000, where xx is time in years since the organization began tracking the foxes. Calculate the average rate of change for the population over the following intervals: [0,10][0,10], [20,30][20,30], [40,50][40,50], [60,70][60,70]. Part A: Over which time interval did the population decline the fastest? Part B: Over which time interval did the population decline the slowest? Select one answer for Part A and one answer for Part B.