l = 20cm, b = 15cm, h = 12cm.
∴ Total surface area of a cuboid
A = 2(lb + bh + lh)
=2(20 × 15 + 15 × 12 + 20 × 12)
= 2(300 + 180 + 240)
= 2 × 720
= 1440 sq.cm.
The cost of painting a cuboid at the rate of 5 paisa per sq. cm for 1440 sq.cm.
= 1440 × 5 paisa
= 7200 paisa
= ₹ 7200/100
= ₹ 72
