Given:
Length, l = 80 cm
Breadth, b = 40 cm
Height, h = 30 cm
Area of the base of the tank = lb
= 80 × 40
= 3200 cm2
Area of side faces = 2bh
= 2 × 40 × 30
= 2400 cm2
And,
Area of the back face = hl
= 30 × 80
= 2400 cm2
Thus, we have:
Area of the paper needed = 3200 + 2400 + 2400 = 8000 cm2