$13-7.$ The East Coasters Bicycle Shop operates $364$ days a year, closing only on Christmas Day. The shop pays $$300$ for a par$-$ ticular bicycle purchased from the manufacturer. The annual holding cost per bicycle is estimated to be $25\%$ of the dollar value of inventory. The shop sells an average of $18$ bikes per week. The ordering cost for each order is $$250.$ Determine the optimal order quantity and the total minimum cost.