b$.$ Compute MAPE for each forecast. $($Round your intermediate calculations to $5$ decimal places and final answers to $4$ decimal

places.$)$

c$.$ Prepare a naive forecast for periods $2$ through $11$ using the given sales data. Compute each of the following; $(1)$ MSE, $(2)$ MAD, $(3)$

tracking signal at month $10,$ and $(4)2s$ control limits$.($Negative values should be indicated by a minus sign. Round your answers to $2$

decimal places.$)$