Question

What is the length to one side of this triangle

Answer 1

The formula of the altitude of an equilateral triangle with side x:
$h=\dfrac{x\sqrt3}{2}$
We have:
$h=6\sqrt3$
Substitute:
$\dfrac{x\sqrt3}{2}=6\sqrt3\ \ \ |\cdot2\\\\x\sqrt3=12\sqrt3\ \ \ |:\sqrt3\\\\x=12$