Please help solve the ff:

The employees of a subsidiary that does asbestos cleanup are being tested for indications of asbestos in their lungs. The firm is asked to send four employees who have positive indications of asbestos on to a medical center for further testing. Suppose 40% of the employees have asbestos in their lungs. Let X; be the number of employees who are screen-tested to find one who has positive indications of asbestos in his/her lungs. a. Let Y be the total number of employees tested to find four with positive asbestos in their lungs. Define Y as a function of X. Using the MGF technique, find the probability distribution of Y. b. Concerned with the cost of screening test, Lee Hu Kay would like to know the maximum number of employees tested to find one who has positive indications of asbestos in his/her lungs (Z). Given X1, X2, X3 and X4, derive the distribution function of Z