Using calculations with conditional rules in form

1. I want the form to submit ONLY when the Total Bottles is a multiple of 6. That means there needs to be a condition to say to Hide the Submit button when the calculation is not met but I can’t see how to do this.
2. When the submit button is hidden, I want the form message to say that orders must be submitted in multiples of 6. I can’t see how to do this.

I have updated the calculations in your form:

The Submit button is being hidden based on the following condition:

Currently, the following Text element is always displayed in the form. If you would like to display this or another element based on a condition, this is also possible.

For your reference, here are links to related user guides:

How to Perform Form Calculation Using a Widget

Conditional Logic for Online Forms

How to Show or Hide Fields Base on User's Answer