Provide explanation on the question below, 

Xcom is a small retailer that sells phone cases. The following estimates are available for the coming period: Month Budgeted Sales (Units) April 40,000 May 50,000 June 44,000 i. Notes: Opening cash balance for the month of May is expected to be $9,250. ii. Inventory policy- ending inventory of finished goods equal to 25% of that month's sales. Budgeted selling price per case- $40 iii. iv. V. vi. vii. Purchase price per case - $10 (purchase volume greater than 30,000 cases per month will receive a 5% discount). Collections from customers: 80% in the month of sale 20% one month after the sale Monthly operating expenses are budgeted at: Marketing $20,000 per month Sales commission (5% of Total Sales Collection for the month) Administration cost per month is $18,000. This includes depreciation of $2,000 per month. All expenses and purchases are paid in the month incurred unless otherwise specified. Required:For the month of May, you have been asked to prepare: a. Purchases budget in units and dollars | b. Sales collection schedule C. Cash Budget d. Explain the meaning of the term 'Rolling Budget'