# Can somone help me solve the length of this side?

Feb 16, 2018

$9$ units.

#### Explanation:

Since, $\triangle D E C$ is similar to $\triangle A B C$,

therefore, the ratio of sides is a constant.

$\frac{A D}{D C} = \frac{1}{3}$

given that AD is 3 units long,

$D C = 3 \times 3$
$= 9$ units.