please help this probability and statistics question with clear steps and also expatiation, thankkk so much

3. In a bolt factory, machines A, B and C manufacture 25, 35 and 40 percent of the total output, respectively. Of their outputs, 5, 4, and 2 percent, respectively, are defective bolts.~ [a] A bolt is chosen at random, what is the probability that the chosen bolt is a defective? (4 marks) [b] Knowing that the chosen bolt is a defective, what is the probability that the bolt came from machine B? (6 marks)