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Step-by-step explanation:

the answer is: 5,953.2 mm²

you have the  8-sided octahedron as a composite figure that has 2 square pyramids. so, you should   apply the formula for the calculated area of a square pyramid as so:   a=s²+2sl

  a is the area of the square pyramid.

  s will be the base of the square pyramid (s = 33 mm).

  l is the slant height of the square pyramid (l = 28.6 mm).

then, when you substitute these values into the formula you get:

  a=s²+2sl

  a=(33 mm)²+2(33 mm)(28.6 mm)

  a=1089 mm²+1887.6 mm²

  a=2,976.6 mm²

thus, the area of the  surface area of the octahedron is:

sa = 2a

sa = 2(2,976.6 mm²)

sa = 5,953.2 mm²

thus the answer will be: 5,953.2 mm²