How do you get the answer to the first part?

Jamike Williams, Incorporated has a policy that requires 20 percent of the expected sales of its product to be on hand at the end of the prior month. Forecasted sales, in units, for the months of January through April are as follows:

January	36,000 units
February	42,000 units
March	58,000 units
April	52,000 units

Required:

1. Calculate the number of units planned for ending inventory for January, February, and March.
2. Calculate the number of units budgeted to be produced in January, February, and March.

	January	February	March
Units planned for ending inventory
Units budgeted to be produced	37,200	45,200	56,800