The real estate assessor for a county government wants to study various characteristics of single-family houses in the county. A random sample of 70 houses reveals the following:
• Heated area of the houses (in square feet):
 = 1,759, S = 380.
• 42 houses have central air-conditioning.
a. Construct a 99% confidence interval estimate for the population mean heated area of the houses.
b. Construct a 95% confidence interval estimate for the population proportion of houses that have central air-conditioning.