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A newspaper reports that the average expenditure on Valentine's Day is $100.89. Do male and female consumers differ in the amounts they spend? The average expenditure in a sample survey of 40 male consumers was $134.67, and the average expenditure in a sample survey of 30 female consumers was $63.64. Based on past surveys, the standard deviation for male consumers is assumed to be $45, and the standard deviation for female consumers is assumed to be $20. (a) what is the point estimate (in dollars) of the difference between the population mean expenditure for males and the population mean expenditure for females? (Use male - female.) (b) At 99% confidence, what is the margin of error (in dollars)? (Round your answer to the nearest cent.) $ (c) Develop a 99% confidence interval (in dollars) for the difference between the two population means. (Use male - female. Round your answer to the nearest cent.) $ to $