I want to know how to calculate Lessopening stock of FG in May as 30 in the second question. Why is this answer 30?

4. Rocky Mountain Construction ... All homes are very similar \& require 10 pallets of wood. They want to keep on hand 60% of next months inventory needs. A pallet of wood costs $2,500. Rocky Mountain pays for the pallets 20% in month of purchase \& 80% in the following month. They are anticipating sales of: May: 8 homes; June: 25 homes; July: 15 homes; August: 22 homes. The company prior to May 1 keeps different inventory levels as there is limited demand and therefore on May 1 beginning inventory is $75,000. The company has different credit terms prior to May 1 , and therefore the opening accounts payable on May 1 was $50,000 a. Prepare a purchases budget for the three months related to pallets of wood(May, June \& July) b.Prepare a schedule of expected cash disbursements for purchases (May, June \& July)