A company that manufactures cell phones has two machines (A) and (B). 54% of the cell phones produced are made by machine (A) and the rest by machine (B). The proportion of defective cell phones by (A) is 0.2 and by (B) is 0.5. (a) What is the probability that a cell phone from that factory is defective? b) What is the probability that, knowing that a cell phone is defective, it comes from machine (A)?