The given information is the quarterly sales of gasoline in the United States (in millions of barrels during part of the 1980s and the 1990s. Estimate the linear trend and use it to forecast sales for the first quarter of 1992. Note: There are two parts to this question. The first answer looks like S = a +b * T where A an B are constants and t is the time period, i.e. t = 17 for the first quarter of 1992. The second answer is the forecast quantity. Second Hint: use Excel.

Time Quantity Time Quantity
1988.1 11 1990.1 14
1988.2 15 1990.2 18
1988.3 12 1990.3 15
1988.4 14 1990.4 17
1989.1 12 1991.1 15
1989.2 17 1991.2 20
1989.3 13 1991.3 16
1989.4 16 1991.4 19