Step 1: Count event A
Prime sums are 2, 3, 5, 7, 11 with \(1+2+4+6+2=15\) outcomes.
Step 2: Count A and B
Outcomes with a prime sum and at least one 5: \((2,5),(5,2)\) with sum 7 and \((5,6),(6,5)\) with sum 11. So 4 outcomes.
Step 3: Conditional probability
\(P(B|A)=\frac{4}{15}\), so \(P(\text{not }B|A)=\frac{11}{15}\).
Step 4: Odds against
Odds against \(B\) given \(A\) are \(\frac{11/15}{4/15}\), that is \(11:4\).
Final Answer:
The odds against are \(11:4\).
\[ \boxed{\text{(A) }11:4} \]