Answer:The cost of the research into the feasibility of renting the sixth floor.
Explanation:
This cost will not considered for it's a sunk cost which was useful in helping the company to take a decision but it's not recoverable, the letting or not letting out of the building cannot change, so it should not be consider when deciding whether to rent out the sixth floor.
The price of renting the sixth floor out impacts on the income and so equally is cost in terms of materials in moving the human resources department, refurbishing the new office and efficiency this makes all these relevant in deciding whether to rent out the sixth floor.