#### Answer

$x = 16.5$

#### Work Step by Step

Since we have the measure of one angle and the measure of the side opposite to that angle, we can use the tangent ratio to find $x$, which is the side adjacent to the given angle.
The tangent ratio is given as follows:
tan $A = \frac{opposite}{adjacent}$
Let's plug in what we know:
tan $36^{\circ} = \frac{12}{x}$
Multiply each side by $x$:
tan $36 ^{\circ}(x) = 12$
Divide both sides by tan $36^{\circ}$:
$x$ = 12/tan $36^{\circ}$
Divide to solve:
$x = 16.5$