Show $me$ the steps $to$ solve: Perform a Trend and Seasonal analysis with the following data. Include the trend formula and the multiplicative indices for the seasons. Using the model forecast sales for the next year $(all4$ seasons $of$ year $4).$

Year Season Sales

$1sp140$

$1su50$

$1w130$

$1f520$

$2sp200$

$2su110$

$2w190$

$2f550$

$3sp260$

$3su220$

$3w210$

$3f570$