Yuestion $111$ puint

A small mail$-$order company uses $15,000$ boxes a year. The holding cost rate is $20$ percent of unit cost per year, and the ordering cost is $$30$ per order. The following quantity discounts are available.

Number of Boxes Price per Box

$1,000to1,999,1\mathrm{.}30$

$2,000to4,999,1\mathrm{.}20$

$5,000to9,999,1\mathrm{.}18$

$10,000or$ more $1\mathrm{.}16$

Determine the optimal order quantity. $$

$2000$

$5000$

$1000$

$10000$