A concert promoter is forecasting attendance. The historical attendance and forecast in the past $4$ periods are given below.

$\backslash$table$[[$Year$,$Attendance,Forecast$],[1,10,000,$No forecast$],[2,12,000,$No forecast$],[3,18,000,16000],[4,20,000,22000]]$

What is the mean absolute deviation based on the forecasts for Year $3$ and $4?$

$1000$

$2000$

$3000$

$4000$