Here we are given that
(i) Length of plastic box (l) = 1.5 m
Breadth of plastic box (b) = 1.25 m
Height of plastic box (h) = 65 cm
= 0.65 m
Since box is open at the top.
Therefore total
surface area of the plastic box (open at the top)
= lb + 2bh + 2hl
= [1.5 x 1.25 + 2(1.25 x 0.65 + 0.65 x 1.5)] m2
= [1.875 + 2(0.8125 + 0.975)] m2
= [1.875 + 2 x 1.7875] m2
= [1.875 + 3.575] m2
= 5.450 m2
Hence, area of the plastic sheet required for making the box is 5.450 m2.
(ii) Cost of 1 m2 plastic sheet = Rs. 20
Cost of 5.45 m2 plastic sheet
= Rs. 5.540 x 20
= Rs. 109