Problem 7 (P7_Data on the template) contains sample data for 400 customers. This company, ElecMart sells electronic appliances for mail-in orders. Consider this data as a random sample from some of ElecMart mail-in orders. Find the following confidence intervals: (20 points) a) Find the 95% Confidence Intervals for the sample mean of the total cost spent by the 400 customers? b) Find the 95% Confidence Interval for the variance of the total cost spent by the 400 customers c) Find the 95% Confidence Interval for the portion of all customers whose order contains at least 5 items and cost at least $100 (Note, use the short form of the Cl proportion formula as