For the models

(1) ????̃???? − 0.5????̃????−1 = ????????

(2) ∇???????? = ???????? − 0.5????????−1

(3) (1 − 0.6????)∇???????? = ????????

write down the forecasts for lead times ???? = 1 and ???? = 2:

(a) From the difference equation

(b) In integrated form (using the ???????? weights)

(c) As a weighted average of previous observations