To classify the number 27 as a perfet square it would mean that if you calculate its square root the result will be a whole number.
If you calculate the square root of 27 you get that it is 5.19615....., the result is not a whole number so you cant classify 27 as a perfect square.
To classify 27 as a perfect cube would mean that if you calculate the cube root of 27, the result will be a whole number:
The result of the cube root of 27 is 3, which is a whole number, so you can classify it as a perfect cube.
The correct option is B.