USA Today reports that the average expenditure on Valentine's Day was expected to be $100.89. Do male and female consumers differ in the amounts they spend? The average expenditure in a sample survey of 58 male consumers was $139.97, and the average expenditure in a sample survey of 31 female consumers was $64.51. Based on past surveys, the standard deviation for male consumers is assumed to be $31, and the standard deviation for female consumers is assumed to be $10. The a value is 2.576. Round your answers to 2 decimal places. a. What is the point estimate of the difference between the population mean expenditure for males and the population mean expenditure for females? b. At 99% confidence, what is the margin of error? c. Develop a 99% confidence interval for the difference between the two population means.