Slope = 29.2
Intercept = 37.7
Deseasonalised Forecast Y = 37.7 + 29.2*t
Now,
For Winter in Year 20XX+1
t = 16
Deseasonalised Forecast = 37.7 + 29.2*16 = 504.9
and,
Seasonal Factor for For Winter in Year 20XX+1 = 1.10
Forecast = Deseasonalised Forecast*Seasonal Factor = 504.9*1.10
Forecast = 555.39
Forecast = 555.4
Period Year 20XX-2 Sales 63 94 118 129 20XX-1 204 215 227 Quarter Spring Summer Fall...