b$.$ Fit a simple linear regression model to the sales data. $($Do not round intermediate calculations. Round your answers to $2$ decimal places.$)$

$$

$$

c$.$ In addition to the regression model, determine multiplicative seasonal indexes. A full cycle is assumed to be a full year. $($Do not round intermediate calculations. Round your answers$$to $2$ decimal places.$)$

$$

b$.$ Calculate the weighted three$-$month moving average for the periods $4-12$using weights of $0\mathrm{.}50($for the period t$1)$; $0\mathrm{.}30($for the period t$2)$ and $0\mathrm{.}20($for the period t$3).($Round your answers to $1$ decimal place.$)$