HTH Manufacturers make bookshelves. The following information was extracted from the budget for the year ended 28 February 2020: Information: The estimated sales for the financial year is 2000 units with a selling price of R600 per bookshelf. Where variable production cost per bookshelf is R180, R120 and R60 for direct materials, direct labour and overheads respectively. In addition, the fixed production overheads amount to R170 000. Sales commission is 10% of sales and the salary of the sales manager is R100 000 per year. 4.2 calculate the break-even value using the marginal income ratio?