Sue and Bob take turns rolling a 6-sided die.  Once either person rolls a 6 the
game is over.  Sue rolls first, if she doesn't roll a 6, Bob rolls the die, if
he doesn't roll a 6, Sue rolls again. They continue taking turns until one of
them rolls a 6.

Bob rolls a 6 before Sue. 

What is the probability Bob rolled the 6 on his second turn?