Given the apothem (a) and the side of the regular polygon, the area (A) of the polygon may be calculated by the formula,
A = aP/2
where P is the perimeter.
Given that the octagon has a length of 11, its perimeter is 88. Substituting this to the formula above,
A = (8.85)(88) / 2 = 389.4
Thus, the area of the polygon is 389.4 unit².
