I'm trying to apply the Bayes Theorem Supplied facts: lab-test produces false negatives 2% of the time and false positives 5% of the time.

Need help thinking through this one. I'm trying to apply the Bayes Theorem

Supplied facts:

lab-test produces false negatives 2% of the time and false positives 5% of the time. Assume that 10% of the employees at this company use drugs.

False Negative = N    0.02                N' correct results ?

False Positives = P     0.05

           Using drugs = D         0.10                Not using drugs = D' 0.90

a.      If an employee tests positive for drug use, what is the probability that he/she does not use drugs? 

P(P|D')*P(D') =

b.    What is the probability a drug user tests negative twice in a row?

c.     A non-drug user was tested positive for drug use. In response to her/his complaint, the company agreed to conduct her/his drug test again. What is the probability that her/his test will turn positive again?