Question

One side of a regular hexagon is 18 cm. which is the perimeter

Answer 1

"Hexagon" means it has six sides.
"Regular" means all of its sides are the same length.

So the perimeter of a regular hexagon is (6) times (the length of any side).

  6 x 18 cm  =  108 cm

Answer 2

6 sides to a hexagon
if one side is 18 cm, then you can solve this by creating the equation:
18*6=108
the perimeter is 108 cm