probability - Expected number of Die Rolls to see repeats

How many rolls of a fair six-sided die must one make, on average, until a 6 has been rolled precisely 6 times?

I worked out that on average number of rolls to roll a single 6 is 6, from the geometric formula of expected value.

However I am stumped on how to go about answering this question for 6 being rolled precisely 6 times.