A wholesale distributor of automobile suppliers find that the number of batteries of a given type she has sold per year during the past seven years and the corresponding values of a certain economic index are as follows Year Sales (1000 units) Economic Index 15.1 87 17.4 122 15.5 119 22.8 150 11.6 93 19.2 124 14.7 115 Year Economic Sales (Y) XY YZ Index (X) 87 15.1 1,313.7 7,569 228.01 122 17.4 2,122.8 14,884 302.76 119 15.5 1,844.5 14,161 240.25 150 22.8 3,420 22,500 519.84 93 11.6 1,078.8 8,649 134.56 124 19.2 2,380.8 15,376 368.64 115 14.7 1,690.5 13,225 216.09 Total 810 116.3 13,851.10 96,364 2010.15 Mean 115.71 16.61 1,978.73 13,766.29 287.16