Final answer:
In incremental analysis for Jobart Company's make-or-buy decision, the opportunity cost of $30,000 from not producing a different product should be added to the 'Make' column, as it is an opportunity lost if the company chooses to make the part in-house.
Step-by-step explanation:
When conducting incremental analysis in a make-or-buy decision, Jobart Company should consider the opportunity cost of using the released productive capacity to generate additional income. Since Jobart can use the capacity to generate an additional income of $30,000 by producing a different product if it buys the part instead of making it, this opportunity cost should be acknowledged in the analysis. Therefore, the correct approach is to add $30,000 to other costs in the "Make" column since this cost is an opportunity lost if the part is manufactured in-house instead of being bought and using the capacity elsewhere.