From 8,900 to 7,380 as a result of eliminating department b, therefore the management of the company is advised not to eliminate dept B.

The problem asks for an operating statement using marginal costing and absorption costing, and a reconciliation statement. However, critical information is missing to complete these statements fully.

Missing Information:

• Selling price per unit: This is required to calculate sales revenue.
• Non-manufacturing costs: (e.g., selling and administrative expenses, variable or fixed) are not provided.
• Production and sales quantities for different periods: The problem states "budget for the manufacture and sales of $20,000$ computers per month," implying that production equals sales. If production equals sales, there are no changes in inventory, and thus, the profit under marginal costing will be equal to the profit under absorption costing. This makes a reconciliation statement trivial (difference will be zero).
• The question asks for "three quarters," but the data is given "per month."

Given these limitations, a complete operating statement and a meaningful reconciliation statement cannot be prepared. However, we can determine the per-unit product costs and total fixed manufacturing overhead based on the provided data.

Step 1: Calculate per-unit product costs.

• Marginal Costing Product Cost (Variable Manufacturing Cost):

  • Direct Materials = $\text{N}500$
  • Direct Labor = $\text{N}200$
  • Variable Overhead = $\text{N}100$ $Variable Manufacturing Cost per unit = N500 + N200 + N100 = N800$

• Absorption Costing Product Cost (Total Manufacturing Cost):

  • Direct Materials = $\text{N}500$
  • Direct Labor = $\text{N}200$
  • Variable Overhead = $\text{N}100$
  • Fixed Overhead = $\text{N}400$
  $$$$