we know that
the distance from the centroid of the triangle to one of the vertices is the radius of the circle required to inscribe an equilateral triangle.
[distance centroid of the triangle to one of the vertices]=(2/3)*h
h=the altitude of the equilateral triangle-----> 21.65 cm
so
[distance centroid of the triangle to one of the vertices]=(2/3)*21.65
[distance centroid of the triangle to one of the vertices]=14.43 cm
the radius is equal to the distance of the centroid of the triangle to one of the vertices
hence
the radius is 14.4 cm
the answer is
the radius is 14.4 cm