A fair die is tossed repeatedly until a six is obtained. Let \( X \) denote the number of tosses required and let \( a = P(X = 3) \), \( b = P(X \ge 3) \) and \( c = P(X \ge 6 \mid X > 3) \). Then \( \frac{b + c}{a} \) is equal to __________.
