What is the base of a regular hexagon

If you already know the length of a side, then you can simply write it down; in this case, the length of a side is 9 cm. If you don't know the length of a side but know the length of the perimeter or apothem (the height of one of the equilateral triangles formed by the hexagon, which is perpendicular to the side), you can still find the length of the side of the hexagon. Here's how you do it:
If you know the perimeter, then just divide it by 6 to get the length of one side. For example, if the length of the perimeter is 54 cm, then divide it by 6 to get 9 cm, the length of the side.
If you only know the apothem, you can find the length of a side by plugging the apothem into the formula a = x√3 and then multiplying the answer by two. This is because the apothem represents the x√3 side of the 30-60-90 triangle that it creates. If the apothem is 10√3, for example, then x is 10 and the length of a side is 10 * 2, or 20.