I'll give you a couple of hints:
I am assuming both locks A and B have the probability of 73% each of waking bob up, that is, p = 0.73
for clock A and p=0.73 for clock B. so the probability of clock A not waking Bob up would be (1-0.73 = 0.27).Same for clock B..
Can you now find the probability that both clocks wont wake bob up?
Probability that A is defective:
Probability that the parts are defective:
Probability that part is defective given it was manufactured on A:
you have to find the probability that the part was manufactured on A given that it is defective, that is, :
Find P(A|D) using CONDITIONAL PROBABILITY