Bob and Jack are standing facing each other. They are told that there are 11 cones divided into 2 colours (black and white). Bob has 6 of those cones behind his back and Jack has 5. None of them can see his own cones but can see the other one's cones. They are also told that the number of the black cones is higher or lower by 1 than the number of the white cones. Each one of them was asked "do you know how many of the cones behind your back are black and how many are white?"
The answers were as follows:

Bob: I don't know.

Jack: I don't know.

Bob: I don't know.

Jack: I don't know.

Bob: I don't know.

Jack: I don't know.

Bob: I know!

How many cones behind Bob's back are black and
how many are white?