SOLVE BY HAND PLEASE $($not excel$)$

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.

Tablet Computer Sales

$\backslash$table$[[$Week$,$Units Sold$],[1,88],[2,44],[3,60],[4,56],[5,70],[6,91],[7,54],[8,60],[9,48],[10,35],[11,49],[12,44],[13,61],[14,68],[15,82],[16,71],[17,50]]$