Let
x---------> the amount of building blocks in each box
we know that
82=2*x+(8+4+6)
82=2*x+(18)
Solve for x
Subtract 18 from both sides
82-18=2*x+18-18
2*x=64
Divide by 2 both sides
x=32 building blocks
therefore
the answer is
the amount of building blocks in each box is 32