Answer
$\left\{-\sqrt{2},\sqrt{11}\right\}$
Work Step by Step
The number $\sqrt{-8}$ is an imaginary number since the radicand (equal to to $-8$) is a negative number and the index (equal to $2$) is an even number.
Irrational numbers are numbers that cannot be expressed as a ratio between two integers. So in decimal form, the decimal value is nonterminating and nonrepeating. Hence, from the given set, $
\left\{-\dfrac{9}{4},-2,-\sqrt{2},0,0.6,\sqrt{11},\sqrt{-8},6,\dfrac{30}{3}\right\}
$ the rational numbers are
\begin{align*}
\left\{-\sqrt{2},\sqrt{11}\right\}
.\end{align*}
