Question

find the area of 4 walls and the floor of a rectangular room

Answer 1

If we look around and observe the walls of a room, we find that generally the walls are in the shape of a rectangle the floor and the ceiling of the room are also of rectangular shape.
Let l, b, h be the lengths of AB,AD and AE as shown in the figure. Here l and b are the length and breadth of the floor and h the height of the room.
For the rectangle ABFE, the lengths of two adjacent sides are l and h. its area = lh
For the rectangle BCGF, the lengths of two adjacent sides are b and h. its area = bh
For the rectangle CDHG, the lengths of two adjacent sides are l and h. its area = lh
For the rectangle DAEH, the lengths of two adjacent sides are b and h. its area = bh
Observe the opposite walls being of the same size and shape have the same area too.

Hence the total area of the four walls = lh+bh+lh+bh
= 2lh+2bh
= 2h(l+b)

Answer 2

Total Surface Area = 2(lb + bh + lh)
Solution of the question = 2(lb + bh + lh) - lb = 2bh + 2lh + lb