Three-Source Posterior After Alert and Failed Clearance

A transaction comes from source A, B, or C with priors 1/2, 1/3, and 1/6. The alert probabilities are 0.2, 0.4, and 0.8 respectively. Conditional on being alerted, the clearance probabilities are 0.9, 0.6, and 0.25 respectively. Given that the transaction was alerted and then failed clearance, what is the posterior probability it came from source C?