Answer:
Income increased by $315,000
Explanation:
Since there is spare capacity available, we assume there are no incremental fixed costs and as such we only analyze relevant variable costs that vary with the order to identify the possible income effect.
Profit per unit = Order Selling price - Direct + Variable costs
Profit = 100 - 12 - 18 = $70
Total profit from the order = 70*4500 = $315,000
We do not include fixed costs as these will have to be paid regardless of the order. These fixed overheads are probably already absorbed fully given the current production level of 84000 units.
Hope that helps.