Seventy five percent of youths ages 12-17 have a systolic blood pressure lower than 136mm of mercury. What is the probability that a sample of 12 youths of that age group will include:
a. exactly 4 who have a blood pressure greater than 136
b. no more than 4 who have a blood pressure greater than 136
c. at least 4 who have a blood pressure greater than 136.