Well the answer is obvious, but since it's biology lets fill this out with punnet squares. fill the punnet square with 'rr' and cross it with 'rr' since both of Marcus and Olivia can't roll their tounge. when you do cross it you'll get 'rr' which also means their childeren won't be able to roll their tounge. I hope this helped, i'm not very good at explaing things :)
