What is JotForm?
JotForm is a free online form builder which helps you create online forms without writing a single line of code. No sign-up required.
At JotForm, we want to make sure that you’re getting the online form builder help that you need. Our friendly customer support team is available 24/7.
We believe that if one user has a question, there could be more users who may have the same question. This is why many of our support forum threads are public and available to be searched and viewed. If you’d like help immediately, feel free to search for a similar question, or submit your question or concern.
I got what you mean but unfortunately we do not have a feature that populates quantity via condition.
This can only be achieved when you modify your form source code and inject custom script to perform such function.
Let us know if you're willing with using your form source code and if you need assistance with the custom script.
Sorry been ages since I have had time to look at this. I would def need assistance with such a code if you offer of help is still on.
Here is our guide on how to embed your form using the full source code:
Once you have your page setup, please let us know and we will be happy to help you with setting up the script to update the fields.
Thank you for using JotForm!