A retail store in St$.$ John's NL$,$ which sells $($among other things$)$ one kind of USB sticks, knows that the annual demand for these USB sticks is constant at $6000$ units$/$year at the selling price $($to end customers$)$ of $$10/$unit$.$ These USB sticks are obtained only from one supplier, who charges a delivery fee of $$70$ for each order, regardless of the number of units delivered. The inventory holding cost rate is calculated based on $6$ percent annual interest rate.

The supplier charges $$8/$unit for $0999$ units ordered, but is willing to give a discount of $5\%$ per unit for orders between $10001999$ units and a discount of $10\%$ per unit for orders of $2000$ units and above.

In order to get the discount of $10\%$ per unit for orders of $2000$ units and above, what is the optimal order quantity?

Question $12$ options:

$1394$

$1357$

$2000$

$2045$