6.(12 pts) a) How many ways are there to select 6 students from a class of 50 to serve on a committee? (4 pts) b) How many ways are there to select 6 students from a class of 50 to hold six different executive positions on a committee? (4 pts) c) How many bit strings of length 20 have equal numbers of O's and 1's? (4 pts)