#### Answer

integer;
rational number;
real number

#### Work Step by Step

Note that:
$-\sqrt{36}=-6$
RECALL:
(1) The set of natural (or counting) numbers: $\left\{1, 2, 3, ...\right\}$
(2) The set of whole numbers : $\left\{0, 1, 2, 3, ....\right\}$
(3) The set of integers: $\left\{...-3, -2, 1, 0, 1, 2, 3, ...\right\}$
(4) Rational numbers are numbers that can be expressed as $\dfrac{p}{q}$ where $q\ne0$.
(5) Irrational numbers are numbers that cannot be expressed as a quotient of two integers.
(6) All the numbers described above are real numbers.
From the descriptions above, $-6$ is:
an integer;
a rational number since it can be expressed as $\dfrac{-12}{2}$; and
a real number