This is more of drupal question rather than CiviCRM. I would restore it from db backup.
Create a test instance and import the database from backup
Export the webform using node export module from test instance
Import the exported file on live using node export module.
For importing submissions you can export the submission form test instance and user ...
In order to multiply/calculate Amounts based on webform fields, try webform_calculator module: https://www.drupal.org/project/webform_calculator
We've made some edits to support amounts being calculated over multiple pages - you can find what we're currently using for our projects here: https://github.com/KarinG/webform_calculator
How it works
The module ...