Please help on part B, and explain how to find each, thank you

Manager T. C. Downs of Plum Engines, a producer of lawn mowers and leaf blowers, must develop an aggregate plan given the forecast for engine demand shown in the table. The department has a regular output capacity of 135 engines per month. Regular output has a cost of $60 per engine. The beginning Inventory is zero engines. Overtime has a cost of $100 per engine. Month 1 2 3 4 5 120 135 140 120 125 6 125 7 140 8 Total 135 1.840 Forecast a. Develop a chase plan that matches the forecast and compute the total cost of your plan. Regular production can be less than regular capacity. (Negative amounts should be indicated by a minus sign. Leave no cells blank - be certain to enter "0" wherever required.) Answer is complete and correct. Period 2 5 Total 120 136 140 120 125 125 140 135 1,040 120 135 135 125 125 135 135 120 0 1,030 10 0 0 5 0 0 5 0 Forecast Output Regular Overtime Output - Forecast Costs Output Regular 0 0 0 0 0 $7,200 8,100 8,100 7.200 7,500 7,500 8,100 8,100 Overtime 0 0 500 0 500 0 0 7,500 0 7.500 S 61.800 1,000 IS 62,800 Total $7.200 8.100 8.600 7.200 8.800 8,100 b. Compare the costs to a level plan that uses inventory to absorb fluctuations. Inventory carrying cost is $2 per engine per month. Backlog cost is $120 per engine per month. There should not be a backlog in the last month. Set regular production equal to the monthly average of total forecasted demand. Assume that using overtime is not an option. (Negative amounts should be indicated by a minus sign. Leave no cells blank - be certain to enter "0" wherever required. Round average inventory row. Inventory cost row, and Total row values to 1 decimal.) Answer is not complete. Period Total 120 135 140 120 125 125 140 135 1,040 135 135 X 135 135 135 1,040 135 x 5 135 0 135 X 15 X -5 X 10 0 -5 0 % Forecast Output Regular Output - Forecast Inventory Beginning Ending Average Backlog Costs Output Regular Inventory Backorder Total