How much cost do I enter for improvement? (Home business)

I have a home office and we did home improvements this year (new wiring and new windows).

When I enter in the improvements in the home office section, do I put the total cost or the % of the home that is my business?

 

Also I do two businesses out of the home office so do I split it even further?

 

For example, the wiring cost $4000. My home office is 10% of the home (sq ft). I do two businesses out of this home office.

 

Do I put $4000 under each home office business? $4000 under one and leave it off the other? $400 under each? $200 under each (splitting the 10% into two?)

 

I called and they helped me find where, but had no idea how and said to "put numbers in and see what happens"???