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:
[tex]\frac{2}{5}+\frac{1}{2}=\frac{4+5}{10}=\frac{9}{10}[/tex]It is rational.
However, let's do the operation.
[tex](2+\sqrt{4})+(15\text{ - }\sqrt{4})=(2+2)+(15\text{ - }2)=4+13=17[/tex]Therefore, it is a natural number and not a rational. The answer is c