What number complete the square x^2 +\- bx

Take 1/2 of b and squaer it so (b/2)^2 would complete the square (sign doesn't matter becaus when squareing, sign goes positive)

The surface area of the pyramid will be given as follows:
Area of triangles:
A=1/2×base×height
A=1/2×12×18
A=108 m²
Area of 6 triangles is given by:
A=108×6=648 m²

Area of the hexagon:
A=6×1/2×12×6√3
A=374.123m²

Total surface area:
SA=648+374.123
SA=1022.123 m²~1022 m²

C] 1022 m²