Is there a way to use the value of DFF using EL in the Page Composer?

Summary:

We are customizing Expense Item using Page Composer.

The requirements are as follows.

1. Automatically enter the "Number of days" value by specifying "From Date" and "To Date"
2. When we enter "Daily Amount", we multiply it with the entered "Number of days" value to automatically enter the "Amount" value

In order to implement the above requirements, we were proceeding as follows.

1. Create "From Date" and "To Date" as DFF
2. Enter the value of "Number of Days" using EL

But we couldn't proceed in process 2.
Because we didn't know how to get the DFF, "From Date" and "To Date" values.

So we would like to ask you a question about this.