By the way, your basic formula is wrong. P(A)*P(B) is "probability of A and B" if A and B are independent events, not "probability of A or B". That is P(A)+ P(B)- P(A and B).
I have no idea what you are doing there. "P(not B)" is NOT P(A) or P(B)/P(B), it is 1- P(B) but, in any case, that has nothing to do with the conditional probability asked for here.(ii)
If a microwave oven is found to be faulty, find the probability that it was produced on line A.
Here i did -
P(not B) = P(A) or P(B) / P(B) = 0.00096 x 0.012 = 0.08
Look at my example above. There were a total of 36 defective ovens, 24 of them from A. If an oven is defective, the probability it was from A is 24/36= 2/3.