The math SAT score of a high school student graduate can be approximated by S(x)=573-133(0.987), where x is the household income of the student in thousands of dollars per year. What is the average rate of change of the SAT score for students with household incomes ranging from $40,000 to $60,000 per year, in points per thousand dollars? Round answers to 3-decimal places and do not include units with your answer.