Answer: $6 per unit on average
Explanation:
Since 60% of the fixed manufacturing overhead can be eliminated when the parts are bought from an outside supplier, therefore (100% - 60%) = 40% are unavoidable when when it buys from suppliers outside.
Therefore, the unit product cost when the parts are bought will be:
= Purchase cost + Unavoidable fixed manufacturing overhead
= $13 + ( 40% * $5 )
= $15
Then, the financial advantage (disadvantage) will be:
= $21 - $15
= $6
Therefore, the correct option is $6 per Unit on average.