Initialize the exponential smoothing with correction for trend model using the

above data. Suppose

$145$ X$1=$

and

$160.$ X $2=$

Apply the model through periods

$1$ and $2$ using

$=0\mathrm{.}2$ HW

and

$=0\mathrm{.}3$ HW

$.$ Calculate one$-$period$-$ahead$-$forecast

errors for periods $1$ and $2$ and using these two forecast errors, calculate the

estimate of the standard deviation of one$-$period$-$ahead forecast error,