Puzzle Details

What shape completes the bottom line?

triangle pentagon square
square hexagon hexagon square
pentagon hexagon hexagon hexagon square triangle
hexagon octagon octagon octagon octagon ==?==

Square the first shape's sides and the remaining shapes add up to this number.

E.g.

triangle pentagon square
>> 3x3 = 5 + 4
square hexagon hexagon square
>> 4x4 = 6 + 6 + 4

Therefore:

hexagon octagon octagon octagon octagon square
>> 6x6 = 8 + 8 + 8 + 8 + 4

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