In the question you have to find whether the number is either rational or irrational.

Square root of 30 is irrational because the answer is a non-terminating decimal.

4/7 is rational because it is a fraction.

21 divided by the square root of 4 is irrational because the result is a non-terminating decimal.

Pi is irrational because it's a non-terminating decimal.

-27 is rational because rational numbers can be positive or negative.

I hope this is correct! :-)