How do I determine the prior odds, and the strength factor, from this information, to determine the confidence the Bob is angry given that his face is red:

You are not sure whether your friend Bob is angry. Generally, Bob is only angry about 2% of the time. But today his face is red. You think the probability that Bob's face would be red if he's angry is about ten times higher than the probability that his face would be red if he's not angry.