Three urns \( A \), \( B \) and \( C \) contain \( 7 \) red, \( 5 \) black; \( 5 \) red, \( 7 \) black and \( 6 \) red, \( 6 \) black balls, respectively. One of the urn is selected at random and a ball is drawn from it. If the ball drawn is black, then the probability that it is drawn from urn \( A \) is:
