The federal reserve system publishes data on family income based on its survey of consumer finances. when the head of the household has a college degree, the mean before-tax family income is $ 84,500. suppose that 60% of the before-tax family incomes when the head of the household has a college degree are between $74,700 and $94,300 and that these incomes are normally distributed. what is the standard deviation of before-tax family incomes when the head of the household has a college degree?