$93.$ A company determines its order quantity for an inventory by using the Economic Order Quantity $("$EOQ$")$ model. The EOQ order quantity for last year was $300$ units while the cost of placing a purchase order was $$50$ and the cost of holding one unit of the inventory per annum was $$15.$ Calculate the number of orders for last year.

a$.30$ orders.

b$.45$ orders.

c$.60$ orders.

d$.90$ orders.