We know that,
According to the question,
Number of white marbles = 6,
Number of red marbles = 5
Total number of marbles = 6 white + 5 red = 11 marbles
(a) If they can be of any colour
Then, any 4 marbles out of 11 can be selected
Therefore, the required number of ways =11C4
(b) two must be white and two red
Number of ways of choosing two white and two red = 6C2 × 5C2
(c) they must all be of the same colour
Then, four white marbles out of 6 can be selected = 6C4
Or, 4 red marbles out of 5 can be selected = 5C4
Therefore, the required number of ways = 6C4+5C4