I The numbers of copies of a college textbook sold quarterly over the past four years has trend and seasonal pattern, to forecast the quarterly,r sales of the textbook, the following regression equation was found: 33:212le I520 erl 1320 one + 290 er3 + 24 r , Where erl , Qty-land er3 are [111]]le variables corresponding to Quarters l, 2 and 3, and f= time period. The sales forecast for Quarter 1 of the next year is ' al.2011 ' b.1232 ' c.1908 ' 12005