Form with limited participants

Form with limited participants

Hello,
I'm a newbie to zoho.
I would like to make a form where people can subscribe for a couple activities. But there can only be 20 participants for each activity. So after the 20nd registration, this choice must be closed... It also needs to show how many empty places there still are for each activty.
Can someone help me out how to make this kind of form with Zoho?


Thanks!!!

Comte