Answer
$\color{blue}{-12, -6, -0.9, -\sqrt{4}, 0, \frac{1}{8}, \text{ and } 6}$
Work Step by Step
The set of integers is: $\left\{...-3, -2, -1, 0, 1, 2, 3, ...\right\}$
The set of rational numbers contain all the numbers that can be expressed as $\dfrac{p}{q}$ where $p$ and $q$ are integers and $q \ne 0$.
Note that:
$-12=\dfrac{-24}{2}$
$-6 = \dfrac{12}{-2}$
$-0.9 = -\dfrac{9}{10}$
$-\sqrt{4} = -2 = -\dfrac{6}{3}$
$0=\dfrac{0}{1}$
$\dfrac{1}{8}=\dfrac{1}{8}$
$6=\dfrac{18}{3}$
The numbers above are quotients of two integers with non-zero denominators so they are all rational numbers.
Thus, the rational among the elements of $K$ are:
$\color{blue}{-12, -6, -0.9, -\sqrt{4}, 0, \frac{1}{8}, \text{ and } 6}$
