Can someone help me? Be details please.

1) A person is exposed to 6.25 rems of radiation. What is the chance that this will result in cancer? (1 Sv = 100 rem)

2)Suppose a scientist places a sample of pure 239Pu in a safe container in her laboratory.She then flies to a distant star in a spaceship that can travel at nearly the speed of light. Once she returns to her laboratory, she discovers that the sample is now only 25%plutonium. How long was she gone as measured in the laboratory frame of reference?