If two dice are rolled together, what is the probability that

If two dice are rolled together, what is the probability that 

a.the total number of spots is 8;

b.the total number of spots is 4;

c.both dice show the same number;

d.at least one of the dice shows the number six?

e.neither of the dice shows the number six?

A coin is to be flipped four times, in sequence.  What is the probability that the number of tails will never exceed the number of heads?   The sequence HHTH satisfies the description, as does HTHT.   However, in each of the sequences THHH and HTTH there is a point at which the number of tails exceeds the number of heads.