Determine the optimal order quantity using the quantity discount model.

Annual demand$-100,000$

The order cost$-$ $$50$

Annual holding rate$-20\%$

Price varies depending on the order quantity per the following

Orders between $1$ to $2,000$ units cost $$12$

Orders of $2001$ to $5,000$ cost $$11$

Orders of $5,001$ and greater cost $$10$

What is the optimal order quantity