Parse calculated values from form to db update api

I have created a serverconnect form with a number of selects.

I can update the db with separate values derived from the selects.

I would like to also apdate the db with the total numeric value of the selects.
I have created a heading which I will hide to calculate the total value.
I have tried creating a variable on the page but cant access that from the server side api

My questions are:

1. Is this the best way of updating the db with the total values?
2. I have given the heading a name, will this enable me to parse its value from the form to the insert data server side api?
3. Can you suggest alternative methods?

Thank you