#### Answer

Option $D$

#### Work Step by Step

The given inequality is "$6$ is less than or equal to $x$".
This is equivalent to "$x$ is greater than or equal to $6$.
The numbers included in this set are the numbers that are greater than or equal to $6$.
The equivalent interval notation of the given inequality will have:
$\bf\text{lower limit:}$
$6$, a bracket will be used since $6$ is included
$\bf\text{upper limit:}$
none, so positive infinity will be used
Therefore, the interval is: $\color{blue}{[6, +\infty)}$