Hi Shikha.. :)
You can think of this problem as:
Rolling two dice repeatedly until the sum of 6 or 7 appears. And then finding the probability that the outcome is T=6.
Let, A be the event that T=6 appears
And B be the event that T=7 or T=6 appears.
Therefore, p= P(A|B) = P(AB)/P(B) = P(A)/P(B) = 5/11
:)