i need help in this assignment

Given:
A figure of a rectangular prism with length l, width w and height h.
To find:
The surface area of the rectangular prism.
Solution:
The product of twice of the length l and the width w is:
[tex]2\times l\times w=2lw[/tex] ...(i)
The product of twice of the length l and the height is:
[tex]2\times l\times h=2lh[/tex] ...(ii)
The product of twice of the width w and the height h is:
[tex]2\times w\times h=2wh[/tex] ...(iii)
The surface area of the prism is the sum of (i), (ii) and (iii). So, the expression for the surface area is:
[tex]A=2lw+2lh+2wh[/tex]
[tex]A=2(lw+lh+wh)[/tex]
Therefore, the required expression is [tex]2(lw+lh+wh)[/tex].