23) B
Probability of false positive on PSA = 0.1 x 0.74 = 0.074
Probability of false positive on DRE = (85 ÷ 1000) x 100 = 8.5% = 0.085
Probability of false positive on both = 0.074 x 0.085 = 0.00629
This gives us a percentage of 0.6% which is 6/100.
So B is the answer.