b$.$ Fit a simple linear regression model to the sales data.

Note: Do not round intermediate calculations. Round your final answers to $2$ decimal places.

c$.$ In addition to the regression model, determine multiplicative seasonal index. A full cycle is assumed to be a full year.

Note: Do not round intermediate calculations. Round your and final answers to $2$ decimal places.

d$.$ Prepare sales forecasts for next year using both of your regression models derived above to show results both with

and without adjustments for seasonality.

Note: Do not round intermediate calculations. Round your final answers to $1$ decimal places.