Demand forecasts for milk bottles in a bottle manufacture are 190, 220, 250, 200 units for day 1, day 2, day 3, and day 4, respectively. A production manager developed the following production plan to satisfy the demand: (1) produce 200 units each day (day 1, day2, day3, day4) using regular time production, and (2) produce 30 units in day 2 and 30 units in day 3 using overtime production. Based on this production plan, what is the total average inventory (the sum of the average inventories over 4 days)?