A regular die is thrown 4 times. Find the probability that:

a.) a 5 will come up all 4 times.

b.) if a 6 is thrown on the first throw, a 6 will also be thrown on the last throw

To a i think its 4C4*(1/6)^4 *(5/6)^0

and to be i think its 4C1*(1/6)^1*(5/6)^3

So umm..help please?