The value of the random value $X$ is the number of throws which are needed to roll a 6 with a fair die.
a) What is the formula for the probability that you will roll your first 6 on the $nth$ throw? (So $P(X=n)$
b) What is the formula for $P(X<n)$, meaning that up to the nth throw at least one 6 is rolled.
c) Express the expectancy (expected value) $E(X)$ as an infinite sum.