9
8 is a multiple and is not a perfect square.
A number that is divisible by 6 but not by 3 must be a multiple of 6 that is not a multiple of 3. Since 6 is a multiple of 3 (6 = 2 * 3), any multiple of 6 will also be a multiple of 3. Therefore, there is no number that is divisible by 6 but not by 3.
25 it is the square of 5 (5x5=25)
you add up the digits, and if the sum is a multiple of 3, then the number is divisible by 3!
9
To square a number you multiple by itself. For instance, 3 x 3 = 9
81 is the square of 9, and is also a multiple of 3 because 3(27) = 81.
9
The result is a square number as for example 3 times 3 = 9 which is a square number
36
36
8 is a multiple and is not a perfect square.
36, 144, 324, 576, 900, ...
Based on your description, it could be 9,4, or 1.
36
14