$($a$)$ What do you understand by a time series forecasting approach? Describe each of the four factors in this approach and indicate how they are determined.

$($b$)$ The historical demand for a product is as follows:

Stating any assumptions that you make answer the following questions.

$($i$)$ Using a weighted moving average with weights of $0\mathrm{.}60$ for June; $0\mathrm{.}30$ for May and $0\mathrm{.}10$ for April, find the July forecast.

$($ii$)$ Using a simple three$-$month moving average, find the July forecast.

$($iii$)$ Using simple exponential smoothing with $\backslash (\backslash$alpha$=0,2\backslash )$ and a June forecast of $13$ find the July forecast. Comment about suitability of your solution. $(7$ marks$)$