How to do more than look up between two forms?

How to do more than look up between two forms?

Dear Zoo team,

I have the following problem to solve in my app:

I have the Expenses form where I put expenses based on Clients and Matters.
In the Expenses view I have activated the sum option and it gives me totals of expenses per client/matter.

Then I have the Billing form where I have the Advanced Expenses, Total Expenses and Outstanding Expenses fields, where the Outstanding Expenses field is a formula based on difference between the Total Expenses from the Advanced Expenses.

I need to make it possible for the total sum of expenses per Client/Matter from the Expenses form view to be inserted automatically in the Total Expenses field of the Billing form.

I would be really grateful if you can give me a hand here.

My app is shared to support at my account. It is called Legal.

Many thanks in advance,

brdgs, Boris :D