Question $2$:

Below is data for tablet computer sales for $17$ weeks

a$)$ Using exponential smoothing, forecast for week $18$ when $a=0\mathrm{.}60,a=0\mathrm{.}70$ and $a=0\mathrm{.}8$

b$)$ Calculate MAD, MSE, and MAPE

c$)$ Which smoothing constant was better and why?

Show your calculation steps.