Given,
l=10 cm, b=20 cm and h=5 cm
The lateral surface area of Cuboid
=2h(l+b)
=2×5(20+10)
=2×5×30
=300 cm2
(Since only the 4 walls are being considered, the 2lb from total surface area has been removed.)
So, total cost required to paint the external areas of 4 walls
=300×10
=₹3,000