4. A research firm conducted a survey to determine the mean amount steady workers spend on cigarettes during the week. They found the distribution of amounts spent per week followed the normal distribution with a population standard deviation o of $5. A sample of 49 smokers revealed that the sample mean (XBAR) = $20. (a) What is the point estimate of the population mean? What is the value of the population mean? (b) Using the 99 percent level of confidence, determine the confidence interval for p. (c) Provide an interpretation for the estimated confidence interval in part b