If we multiply 20 by squareroot 6, the answer would be 20(squareroot6). So it is a rational numbersquare root.
But in a, if we multiply 0.25 that is 1/4, by 15 it will be 15/4, so. itis a rational number
In b:

It is rational.
However, let's do the operation.

Therefore, it is a natural number and not a rational. The answer is c