Answer:
Incremental operating income  = $71,400
Explanation:
Unit variable cost = 18.10 + 7.4+ 5.20 + 5 = $35.7
Note that the $5 additional variable cost was necessitated by the special order , hence it was added
Sales from special order = ( 8,000× $50)           400,000
Variable cost     ( 8,000 ××  $35.7                ( 285600 )
Cost of special machine                         (43,000)
Incremental operating income                    71,400
Incremental operating income  = $71,400
Note that the fixed costs were not considered in the analysis , this simply because they are not relevant to the special order decision.. They would be incurred either way, whether the special order is accepted or not