To find the 9's complement of a number, we subtract each digit from 9.
Given the number is 33, we can find its 9's complement as follows:
The first digit of the number is 3. To find its 9's complement, we subtract 3 from 9: 9 - 3 = 6.
The second digit of the number is also 3. Again, we subtract 3 from 9: 9 - 3 = 6.
Therefore, the 9's complement of 33 is 66.
Option C) 66 is the correct answer.