Answer
$x=5$
Work Step by Step
The function is $k(x)=6x-12$
Substitute $18$ for $k(x)$ to get
$18= 6x-12$
Adding $12$ to both sides of the equation, we have
$18+12=6x-12+12$
$\implies 30=6x$
Dividing both sides by $6$, we obtain
$\frac{30}{6}=\frac{6x}{6}$
Or $5=x$
When $x=5$, $k(x)=18$
