Step 1: Using the formula for \( P(A \cup B) \).
We can calculate \( P(A \cup B) = P(A) + P(B) - P(A \cap B) \). Using the given information, \( P(A \cap B) = P(B/A) \times P(A) \).
Step 2: Conclusion.
Thus, the correct answer is option (C).
Final Answer:
\[
\boxed{\text{(C) } \frac{91}{180}}
\]