Please explain how you are supposed to get the add: desired finished goods units and less: beginning finished goods units. I do not understand at all and need a written explanation that will be easy to understand.

Production Budget (2 of 2) Hayes believes it can meet future sales needs with an ending inventory of 20% of next quarter's budgeted sales volume. Production Budget by Quarteir For the Year Ending December 31, 2020 3 4 Year Expected sales in units Add: Desired finished 3,0003,5004,0004,500 800 Goods units Total required units Less: Beginning 700 900 1,000 3,7004,3004,9005,500 Finished goods units 600 700 800 900 Required production units 3,1003,6004,1004,600 15,400