$Volumeofthebox=Length\times Breadth\times Height$
                             $=6m\times 4m\times 5m$
                             $=120m^3$
Therefore, volume of the box will be $120m^3$.

Given: Perimeter = 16 cm
Perimter of a square = 4 $\times$ Side
$\Rightarrow$ 16 cm = 4 $\times$ Side
$\Rightarrow$ Side $=\frac{16}{4}=4cm$
Area of a square = Side $\times$ Side
$\Rightarrow$ Area of the square $=4cm\times 4cm=16c{m}^2$

We know that 1 m = 100 cm
$\Rightarrow$ 0. 8 m = 0.8 $\times$ 100 cm = 80 cm
Perimeter  = Sum of all sides = AB + BC +AC
$\Rightarrow$ Perimeter = 50 cm + 40 cm + 80 cm = 170 cm
                   

Given: Dimensions of a brick is $20cm\times 10cm\times 5cm$.

Volume of the brick $=length\times breadth\times height=20cm\times 10cm\times 5cm=1000c{m}^3$
Volume of two bricks  $=2\times 1000c{m}^3=2000c{m}^3$
 

Given:
Breadth of a rectangle = 7 cm
Area of the rectangle   = 63 $c{m}^2$

Area of rectangle = Length $\times$ Breadth 
$\Rightarrow$ Length = $\frac{Area}{Breadth}$
$\Rightarrow$ Length = $\frac{63c{m}^2}{7cm}=9cm$

Given: The length of the sides of each square is 10 cm. 
For the rectangle formed:
Length = 10 cm + 10 cm = 20 cm
Breadth = 10 cm
Area of the rectangle = Length $\times$ Breadth = $20cm\times 10cm=200c{m}^2$