Answer:
this is an example of the prisoners' dilemma and the Nash equilibrium:
prisoner 1
confess not confess
3 / 6 /
confess 3 1
prisoner 2
1 / 2 /
not confess 6 2
The dominant strategy for both prisoners will be to confess, since the expected time in jail is lowest = 3 + 1 = 4 years.
If a prisoner does not confess, the expected time in jail would be 6 + 8 = 8 years.
So a Nash equilibrium exists when both prisoners confess.