Adobe Captivate 7 - control of the visibility of two navigation buttons depending on clicking the "send answers"-button

Hello,

How can I realize the following:

The navigation of my e-learning consists of two arrows. By clicking the one you can go forward, by clicking the other you can go backward.

When the users reaches a Drag and Drop-exercise slide within the e-learning he shouldn't go backwards or forwards so the navigation should be disappear. The learner has to answer the drag and drop exercise by clicklng the button "send answer" . After this the navigation should appear.

I already un-click the checkbox for the two arros "visible in the output" in the Settings for the Group which contains the two arrows, so they are not visible in the output at the moment

How to go on?

I think I have to combine the button "send answer" with an action, but I can't assign an action to the button "send answers".

So do I have to assign an action to the slide? But which one?

Thanks for your help!

Greetings

Erica