Prizes in a raffle are determined by taking a ball from a bag. There are 15 balls in the bag, 12 of them are green, two of them with black stars. There are two silver balls, one with a black star, and one gold ball. If you draw the green ball, without the black star, you win a small prize. If you get a green ball with the black star, you get a medium prize. If you get the silver ball without the star, you get a large prize. If you get the silver ball with the black star, you get the extra-large prize. If you get the gold ball, you get the super deluxe prize. If you get a ball, what is the probability of getting the green with the black star?