.
There are two totally different problems in this post.
Therefore, I will answer (b), (c) and (d) ONLY (since these three parts logically comprise one problem)
The probability to get the sum of 7 at each single roll a pair of dice is
( since there are 36 outcomes, in total, and only six are successful,
(1,6), (2,5), (3,4), (4,3), (5,2), and (6,1) ).
So the answers (and the solutions) are
(b) P =
= 0.03215.
(c) P = 1 -
= 0.598122.
(d) P =
+
= 0.803755.