11-7. An article in the Tappi Journal (March 1986) presented data on green liquor Na2S concentration (in grams per liter) and paper machine production (in tons per day). The data (read from a graph) follow: (a) Fit a simple linear regression model with y= green liquor Na2S concentration and x= production. Find an estimate of 2. Draw a scatter diagram of the data and the resulting least squares fitted model. (b) Find the fitted value of y corresponding to x=915 and the associated residual. (c) Find the mean green liquor Na2S concentration when the production rate is 960 tons per day