AFG Company supplies an electronic amplifiers to a company that incorporates these amplifiers to C units and other home appliances. The annual demand for these amplifiers is $4000$ units, and this is co of ant throughout the year. The cost per unit is S$10,$ and the inventory holding rate is estimated to be $5\%$ of the unit cost. The ordering cost per order is $$40$ per order.

$*$To minimize cost, how many units should be ordered each time an order is placed?

$*$Estimate the ordering cost, holding cost, and the total cost if co as are minimized?

$*$Suppose that the company was ordering $1200$ unit per order, what is the total cost under this policy and by how much it will be higher$/$lower than the total cost in b$?$

$*$For the ordering policy in c to be optimal, how much should be the ordering cost per order?