An online clothing store carries three brands of the jeans. 40% of their jean sales are brand A, 20% are brand B and remainder are brand C. 20% of brand A's jeans cost over $100, 40% of brand B's jeans cost over $100 and 90% of brand C's jeans cost over $100. Given that the pair of jeans is bought for over $100, what is the probability that they are brand A? show your work.