860.55 mm
Explanation:
The surface area of an hexagonal prism, also known as an octahedron, is given by the following formula (since we have the apothem):
S= 6*b*(a+h)
where b = is the side of the base, a is the apothem length, and h = the height
S = 6 * 8 * (4√3 + 11) = 48 * 17.92812 = 860.55 sq mm
Could have also have used another formula without the apothem:
S =3 * √3 * b² + 6 * b * h
S = 3 * √3 * 8² + 6 * 8 * 11 = 3√3 * 64 + 528 = 332.55 + 528 = 860.55 sq mm
