probability of cancer

The PSA test is a simple blood test for prostate cancer in men. It is cheap,
but it is not very accurate. According to:
The PSA, prostate cancer and you – VCU Department of Family Medicine
if 100 men are considered:
(a) How many have cancer?
(b) Of those with cancer, what percentage test positive? What is the rate
of false negatives in the population of men with cancer?


I don't know where to start! Please guide me step by step.
Thanks a lot.

there is a yellow box in the middle of the article. 100 people are in the box. How many of them have cancer?