Help with this statistics problem:

EXERCISE 6-17 A cancer researcher wants to test a new combination of chemotherapy and radiation on skin tumors in laboratory mice. The researcher administers the treatment to each of four laboratory mice having the type of skin tumor under study. After a week of treatment, the researcher records failure or success for each mouse, depending on whether or not skin tumor cells are observed on the animal. a. Write down a sample space for this problem, where an outcome shows success or failure for each of the four animals in the experiment. b. Suppose that the treatment combination has no effect on the skin tumors. However, there is a .1 probability that the tumor will disappear spontane- ously over a week of observation. If the mice are independent of one an- other with regard to disappearance of the skin tumor, find the probability function for the sample space in this problem. c. With the probability model above, what is the probability that three or four of the mice will be free of skin tumors at the end of the week of treatment? What is the probability that one or none of the mice will be free of skin tumors at the end of the week of treatment? d. Define a random variable X to be the number of mice that are free of skin tumors at the end of the week of treatment. Find the values X takes on and the probability that X takes on each of these values. Find the expected value, variance, and standard deviation of X