Hi Ria,
You can do this using Button objects that have the toggle property. And then you can ask those buttons how many are "selected" (aka in the down state). There's a slightly more programmatic way to handle the counting with tags, a for loop, and component blocks, but I'm not sure it's worth doing unless you have a really high number of items that make choosing the individual items in the actions quite onerous (in this particular case, something like 20). If anyone's curious how to do that, let us know.
Here's a video -
https://share.smartbuilder.com/public/support/toggle-button-example.mp4Sample lesson attached.