$[15$ points$]$ An assistant manager of an Electronic device retailer is reviewing the costs associated with the store's best$-$selling computers. The data available follows:

Demand $=1200$ units$/$ year

Order cost $=$$$400/$order

Holding cost rate $=20\%/$ear

Unit cost $=$$$850$

a$.$ What is the Economic Order Quantity $($EOQ$)?$ Show all calculations to earn full credit.

b$.$ What is the ordering cost? Show all calculations.

c$.$ What is the inventory holding cost? Show all calculations.

d$.$ If the order quantity is $100$ units, what is the total cost? How does it compare with the total cost for ordering EOQ?