10.21. According to the U.S. Census Bureau, in 2000 the population median income was estimated to be $29,661 for white females, $25,736 for black females, $40,350 for white males, $30,886 for black males. Compare the difference in median incomes between males and females for

(a) white subjects

(b) black subjects. If these are close estimates of the population medians, explain why there is interaction and describe its nature.