forced navigation or activating NEXT button

Hi all, I have a multiple choice question (4 radio buttons) and a submit button to confirm the selection one way or another. I am applying forced navigation to the page; so I have a NEXT button that is by default greyed-out and inactive. I can get the NEXT button to activate (un-grey itself) when the correct answer is selected or when the SUBMIT button is selected.

However I cannot get that action to occur after a selection has been made and the SUBMIT button is clicked.

I guess I need some way of checking which radio button has been selected and if it's the correct one then after the SUBMIT button is selected the the next BUTTON becomes active.

I can get this same principle to work on a simple True/False question without an SUBMIT button.

Any help would be appreciated.

Regards