How to setup a calculation in expenses

Summary:

Calculation in expenses

Content (required):

We need to be able to reimburse expenses made for Home charging of electricity for electrical cars.

How can we do a calculation in the expenses : people should enter KWhrs.

Currently I use Expense Category 'Miscellaneous'. And I made a special Policy to associate with the Expense Type.

I also created a Descriptive Flexfield for Expense Report to enter the KiloWatt Hours.

But when I try to create an expense item, I don't see any calculation. There are also required fields visible that I cannot disable. Can you please assist in making this work?