Demand for stereo headphones and MP3 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 last year was as follows: MONTH DEMAND (UNITS) January February 4,240 4,340 March 4,040 April 4,440 May 5,040 June 4,740 July 5,340 August 4,940 September 5,440 October 5,740 November 6,335 December 6,030 a. Using linear regression analysis, what would you estimate demand to be for each month next year? (Do not round Intermediate calculations. Round your answers to 2 decimal places.) Month Forecast January February March April May June July August September October November December b. To be reasonably confident of meeting demand, Nina decides to use 4 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