Statistics Part 1

Consider a set of 3n numbers having variance 4 . In this set, the mean of first 2n numbers is 6 and the mean of the remaining n numbers is 3 . A new set is constructed by adding 1 into each of first 2n numbers and subtracting 1 from each of the remaining n numbers. If the variance of the new set is k, then 9k is equal to ..........