Demand for stereo headphones and music players for joggers has caused Nina Industries to grow almost 50 percent over the past year. The number of joggers continues to expand, so Nina expects demand for headsets to also expand, because, as yet, no safety laws have been passed to prevent joggers from wearing them. Demand for the players for this year was as follows: MONTH January February March April May June July August September October November December DEMAND (UNITS) 4,130 4,230 3,930 4,330 4,930 4,630 5,230 4,830 5,330 5,630 6,230 5,930 a. Using linear regression analysis, what would you estimate demand to be for each month next year? Using a spreadsheet, follow the general format in Exhibit 3.8. (Do not round intermediate calculations. Round your answers to 2 decimal places.) Month Forecast | May June July August September October November December b. To be reasonably confident of meeting demand, Nina decides to use 2 standard errors of estimate for safety. How many additional units should be held to meet this level of confidence? (Do not round intermediate calculations. Round your answer to the nearest whole number.) Additional units