If you join the 3 diagonals of a regular hexagone, you'll divide it into 6 equilateral triangles. Let's calculate the area of one equilateral triangle:
side = 8 mm,
apothem (= Altitude) = 6.9 mm,
since the area of a triangle = side x altitude (opposed to this side)/2, we can write:
Area = (8 x 6.9)/2, but we have 6 identical triangles, then Total area :
Total Area = 6[(8 x 6.9)/2]/2 = 166 mm² (rounded to the nearest unit)