How can I change the excel function?

Q) In one modification of the Starball production scheduling problem, the maximum storage constraint and the holding cost are based on the average inventory (not ending inventory) for a given month, where the average inventory is defined as the sum of beginning inventory and ending inventory, divided by 2, and beginning inventory is before production or demand. Modify the model with this new assumption, and use Solver to find the optimal solution. How does this change the optimal production schedule? How does it change the optimal total cost?

B C D E F G H 1 Multiperiod production model 2 3 $12.75 4 $12.81 5 $12.87 $12.90 3 Input data 4 Initial inventory (1005) 5 Holding cost as % of prod cost 6 7 Month 1 2 8 Production cost/unit $12.51 $12.54 9 10 Production plan (all quantities are in 100s of footballs) 11 Month 2 12 Units produced 160 200 13 14 Production capacity 3 00300 15 16 On hand after production 200 200 3 300 4 4 300 5 250 200 300 300 300 300 350 350 250 200 17 18 Demand 200 150 300 350 200 19 20 Ending inventory 0 50 50 0 21 22 Storage capacity 100 100 100 100 100 100 23 24 Summary of costs (all costs are in hundreds of dollars) 25 Month 2 3 4 5 6 Totals 26 Production costs $2,001.60 $2,508.00 $3,825.00 $3,843.00 $3,217.50 $2,580.00 $17,975.10 27 Holding costs $0.00 $37.62 $38.25 $0.00 $0.00 $0.00 $75.87 28 Totals $2.001.60 $2.545.62 $3,863.25 $3,843.00 $3,217.50 $2,580.00 $18,050.97 Objective to minimize 29 30 31 Max End Inventory 50 32 B C D E F G H 1 Multiperiod production model 2 3 $12.75 4 $12.81 5 $12.87 $12.90 3 Input data 4 Initial inventory (1005) 5 Holding cost as % of prod cost 6 7 Month 1 2 8 Production cost/unit $12.51 $12.54 9 10 Production plan (all quantities are in 100s of footballs) 11 Month 2 12 Units produced 160 200 13 14 Production capacity 3 00300 15 16 On hand after production 200 200 3 300 4 4 300 5 250 200 300 300 300 300 350 350 250 200 17 18 Demand 200 150 300 350 200 19 20 Ending inventory 0 50 50 0 21 22 Storage capacity 100 100 100 100 100 100 23 24 Summary of costs (all costs are in hundreds of dollars) 25 Month 2 3 4 5 6 Totals 26 Production costs $2,001.60 $2,508.00 $3,825.00 $3,843.00 $3,217.50 $2,580.00 $17,975.10 27 Holding costs $0.00 $37.62 $38.25 $0.00 $0.00 $0.00 $75.87 28 Totals $2.001.60 $2.545.62 $3,863.25 $3,843.00 $3,217.50 $2,580.00 $18,050.97 Objective to minimize 29 30 31 Max End Inventory 50 32