Material Purchases budget

Hello, Hoping you could help me with the working for a P1 pearson mock question.. A company has a production budget for the next 2 years of 36,000 units per annum to be produced evenly throughout both years. Each unit uses 2 kg of material. The estimated opening raw material inventory at the start of the next year is 2,000 kg but the company then wants to hold sufficient raw material inventory at the end of each month to cover the following month's production. The budget material cost is $12 per kg. What is the material purchases budget for next year ? Give your answer to the nearest $000. Answer is 888 However I'm getting 912 My working was Required stock = 36000 units * 2kg = 72000 + 1 month's holding stock = 3000 * 2kg = 6000 Less 2000kg closing stock = 76000kg required x £12 = 912000 Not sure why the mock has 888000 Many Thanks James