Question 1011926
Each side is  {{{27/3=9}}} cm.


An altitude separates two congruent special right triangles.  The altitude serves as height and the hypotenuse is also 9 cm.  The short leg will be half the hypotenuse, or  {{{9/2}}}.


You want an area   {{{2(1/2)(9/2)*y}}},  using y as the altitude.  The factor 2 is used on the far left because TWO of the special 30-60-90 right triangles make your given one equilateral triangle.


find y using pythagorean theorem formula.
{{{y^2+(9/2)^2=9^2}}}