Buena Manufacturing has sales of £850,000. It used materials of £450,000 and direct labour of £175,000, and incurred other variable manufacturing expenses of £30,000. The business also incurred fixed non-manufacturing expenses of £65,000 and selling and administrative expenses of £40,000. Its opening stock of finished goods was £120,000 and its closing stock had reduced by £25,000. Calculate:

• Cost of production • Cost of sales • Contribution margin • Operating profit