A bag contains 15 marbles: 10 red, and 5 white. Furthermore, every marble is labelled: each number in the set {1,2,..., 15} appears exactly once. Suppose four marbles are to be selected from the bag. (i) How many different selections of size 4 are possible? (ii) How many selections consist only of red marbles? (iii) How many selections of size 4 consist of 2 red and 2 white marbles?