Given that,
External length = 80 cm
External width = 65 cm
External height = 45 cm
We know that,
Volume of cuboid = Length × Breadth × Height
Therefore,
External volume of the box = 80 × 65 × 45
= 234000 cm3
It is also given that,
Thickness of the wood = 2.5 cm
Therefore,
Internal length = 80 – (2.5 × 2) = 75 cm
Internal width = 65 – (2.5 × 2) = 60 cm
Internal height = 45 – (2.5 × 2) = 40 cm
As we know that,
Volume of cuboid = Length × Breadth × Height
Therefore,
Capacity of box = Internal volume of the box = 75 × 60 × 40
= 180000 cm3
Hence,
Volume of wood = External volume – Internal volume
= 234000 – 180000
= 54000 cm3
It is also given that,
100 cm3 of wood weighs 8 g
Therefore,
Weight of wood = \(\frac{54000}{100}\times8\)
= 4320 g
= 4.32 kg