Area = (1/2)(apothem)(perimeter)
we are given the apothem, the perimeter is just the length of all the sides.
let A be the apothem, and P be the permeter.
then A = 3
and P = 6*2sqrt(3) = 12sqrt(3)
so we have,
Area = (1/2)AP
.......= (1/2)*3*12sqrt(3) cm^2
.......= 18sqrt(3) cm^2
see Area of a Regular Polygon and Regular polygon area formula for more info