Answer:
$25
Step-by-step explanation:
Based on the information given if it was estimated that it will cost the amount of $40 in order to assemble the costume which means that After spending the amount of $40 on the costume and you realize that the additional pieces that you will need will still cost extra amount of $25 , that simply means that the MARGINAL COST of you completing the costume will be the extra amount of $25 .