For the first one, I think you just calculate probabilities of all X's and compare them to find the biggest ie. X = 1.
P(X=1) = 0.25
P(X=2) = 3/14
P(X=3) = 5/28
P(X=4) = 1/7
P(X=5) = 3/28
P(X=6) = 1/14
P(X=7) = 1/28
For part 2, just add up X = 5,6,7 to get your answer.
[Edit: I'll double check...