steady monthly demand for the electrical power supply unit was $250$ units. selling price was R$80000$ and a mark$-$up of $60\%$ on cost was used. all sales are on credit and the collection period is $90$days. collection costs of approximately R$100$ per unit sold were incurred. annual holding cost of an electrical power supply unit was $0\mathrm{.}24\%$ of the unit cost of the item. cost of placing an order for electrical power supply unit was R$50.$ the cost of capital was $15\%.$ after two months of employment mariam dube made the following proposal