Finding the Third Side of Triangle

Triangle XYZ has one angle measuring $60^{\circ}$ and two sides measuring 9 cm and 12 cm. The side opposite to the $60^{\circ}$ angle is...

What is the length of the third side of triangle XYZ if the side measuring 12 cm is adjacent to the $60^{\circ}$ angle?

Use the Law of Cosines, which states that for any triangle with sides $a$, $b$, and $c$ (where $c$ is opposite angle $C$), the following holds:

$$c^2 = a^2 + b^2 - 2ab \cos(C)$$