A linear trend forecast is shown below (round b & a to two decimals):

		t	Y	t*Y	t2
		1	19	19	1
		2	18	36	4
		3	15	45	9
		4	20	80	16
		5	18	90	25
		6	22	132	36
		7	20	140	49
		28	132	542	140

For Sept., t = 8, and Y_t = 16.86 + 0.50(8) = 20.86 = 20,860

c. The linear trend approach seems to be the least appropriate because the data appear to vary around an average of about 19 [18.86] and because the slope is close to zero (0.50).

d. Sales are reflective of demand (i.e., no stockouts or backorders occurred).