Answer:
Differential income = $960
Explanation:
In a special order decision , the offer should be accepted if the sales revenue from the order is greater than the relevant costs of the special orders.
The relevant costs of the special order = variable cost + additional cost of special stitching machine
                                             $
Sales revenue   (120× $18)                      2,160   Â
The relevant costs of the special order
= (120×8) + (120×2)                            (1,200)
Differential income                             960