Change state of Next button when user visits 3 of 7 layers.

It works in the attached file.

• I used a single object for each tab, rather than a group. (You don't need a shape and a text box. Just put the text in the shape.)
  • Each tab has a Visited state (instead of Selected). Visited is a built-in state, so the tabs will automatically change to that state when clicked. And they'll stay in that state (unless a trigger changes them). 
    • Note: An object will change to Selected if it has that state. But then it will change back to Normal (or to Visited, if it also has that state) if clicked again. Thus, in this case, Visited works better to control the variable.
  • IMHO, the dark rectangles that link the tabs with the circle don't need to be clickable. They're just background graphics. However, if you really wanted them to be part of the tab, you could paste them into the states. 
  • You'll notice that I gave the tabs meaningful names. That makes it much easier to program and troubleshoot. It's a best practice to give everything a meaningful name--especially if you're asking for help with a file. 
• There's a number variable called layerCount, with a default value of 0. 
• Each tab has a trigger that adds 1 to the variable with the condition that the tab is not Visited. Thus, it will only add 1 the first time the object is clicked. 
• The base has a trigger that changes NEXT to Disabled when the timeline starts with the condition that the variable < 3. Thus, it will only disable NEXT before the user finishes watching three layers.
• Each layer has a trigger that changes NEXT to Normal when the media completes with the condition that the variable = 3. 

You'll need to double-check that the slide works. (I did some testing, but with some changes so it didn't require me to listen to all the audio.)

Thank you SO MUCH. Exactly what I was hoping for. I appreciate the explanation as well.