A box made of sheet metal costs Rs 1620 at Rs 30 per square metre. If the box is 5 m long and 3 m wide, find its height.
Given,
Total cost of box made of sheet metal = Rs. 1620
Cost of per square meter metal = Rs. 30
∴ Area of box = 
= 54 m2
Dimensions of box = 5m × 3m × height
Let height of box = h meter
Total surface area of sheet = 2 (lb + bh + hl)
= 54 = 2 (5 × 3 + 3h + 5h)
= 
= 15 + 8h
= 8h = 27 – 15 = 12
= h = 
Height of box = 1.5 meter.
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