24. An established photo processing laboratory has experienced a consistent decline in business, owing primarily to the spread of 1-hour photo processing minilaboratories. The following data represent quarterly sales (in thousands of dollars) for the past 2 years.

a. Average the first year's sales to determine the height of one point on a trend line. (The x value will be 2.5.) Average the second year's sales to determine a second point. Develop an equation for this trend line.

b. Determine the average seasonal index for each of the four quarters of a year, as the ratio of the actual sales value to the trend value.

c. Using the trend formula and the indices developed above, forecast quarterly sales for the following year.

QUARTER SALES 12345678 400 406 446 352 328 320 340 8 264