Current Attempt in Progress

The forecast value for September was $21\mathrm{.}1$ and the actual value turned out to be $18.$ Using exponential smoothing with $=0\mathrm{.}30,$ the forecast value for October would be $q,$

$21\mathrm{.}00$

$20\mathrm{.}17$

$18\mathrm{.}93$

$17\mathrm{.}07$

$18\mathrm{.}09$