4 12 points) Data on the weekly sales of a major brand of canned tuna by a superna med chain in a large midwestern U.S city during a recent calendar year are contained in the file tuna.dat. There are 52 observations on the variables Sai = unit sales of brand No. 1 canned tuna Apr1 = price per can of brand No. 1 canned tuna Apr2,3 = price per can of brands Nos. _ and 3 of canned tuna Disp = a dummy variable that takes the value : if there is a store display for brand No.1 during the week but no newspaper ad; 0 otherwise. DispAd = a dummy variable that ta es the value 1 if there is a store display and a newspaper ad during the week, 0 otherwise. (a) Estimate by least squares, the log-linear model. In(S ) ) = B- BAP BAP 2- BAp )+ 6Dip . B DipAuse ( compute 2 pol. ts+1) (b) Interpret the estimate of 12 (2 points