(i) Lenth of plastic box l = 1.5 m, breadth b = 1.25 m height h = 65 cm = 0.65 m
Area of sheet required for making a plastic box = total surface area of box – Area of top of box
= 2(lb + bh + hl) – lb = 2(1.5 × 1.25 + 1.25 × 0.65 + 0.65 × 1.5) – 1.5 × 1.25m²
= 2(1.875 + 0.8125 + 0.975) – 1.875 m²
= 2(3.6625) – 1.875 m²
= 7.325 – 1.875 = 5.45 m²
Hence, the area of the sheet required for making the box is 5.45 m².
(ii) Total cost of cheet = Rs 20 × 5.45 = Rs 109.