An interest group hires people to solicit donations by telephone. After a brief training period they make calls to potential donors and are paid on a commission basis. Experience indicates that early on, these people tend to have only modest success and that 70% of them give up their jobs in their first two weeks of employment. The group hires six people which can be viewed as a random sample. What is the probability that at least four of the six will give up in the first two weeks?