Suppose that a factory has two machines, machine A and machine B, both producing phone touch screens. 40% of their touch screens come from machine A and 60% of their touch screens comes from machine B. 10% of the touch screens produced by machine A are defective and 5% of the touch screens from machine B are defective. If randomly touch screen has been chosen and it is defective, what is the probability that it came from machine A? Show full answer.