Answer:
a.Economic Order Quantity = Â 4,000 units
b.Total Inventory Cost = Â $7,200
Explanation:
Economic Order Quantity = √(2×Annual Demand×Set-up Cost per Order) / Holding Cost per Unit
                     = √(2×40,000×$180×2)/($12×15%)
                     =  √16,000,000
                     =  4,000
Total Inventory Cost = Set Up Cost + Holding Cost
                 = ((40,000/4,000)×($180×2))+((4,000/2)×($12×15%))
                 = $3,600 + $3,600
                 = $7,200