An operation analyst is forecasting this year's demand for one of his company's products based on the following historical data:

YEAR QUANTITY SOLD

Four years ago $10,000$

Three years ago $12,000$

Two years ago $18,000$

Last year $20,000$

What is this year's forecast using the least squares trend line for these data?

Multiple Choice

$20,000$

$21,000$

$23,000$

$24,000$

$22,000$