In this Excel file, you will find the sales data of a particular model of an electronic calculator for the past $20$ years. Open the spreadsheet and complete the orange colored cells using the Holt's forecasting method with Alpha $0\mathrm{.}3$ and Beta $0\mathrm{.}2.$ The rest of the cells were calculated for you.

What is the forecast for period $21?$ ANSWER:

$[243,238,234,233,248]$

What is the Mean Absolute Error $($MAPE$)$ of the estimation:

$[5\mathrm{.}6\%,2,8\%,3\mathrm{.}3\%,4\mathrm{.}1\%,3\mathrm{.}1\%]$