How can I post the calculation of number of submissions into the calculation field?

I would have received the submissions say on number of attendees...
How would I bring those numbers to the form and limit based on an upper limit of submissions.

You can use the Submission Counter Widget to show how many submissions you take. If you want to learn more about the widget, you can visit the following link: https://widgets.jotform.com/widget/submissions_counter 

I tried to use this widget with the clone of your form. (https://form.jotform.com/92172618485969) I put the condition that allows that if the submission number exceeds the "specific value", it will hide all fields of the form.

Also, you can check out and can do some arrangements with cloning my form.

https://www.jotform.com/help/42-How-to-Clone-an-Existing-Form-from-a-URL

If you require further assistance feel free to let us know.