A room is 8 m long, 6 m wide and 4 m high. It has one door measuring 2 m by 1.5 m and two windows each measuring 1.5 m by 1 m. What is the cost of painting only the four walls at ₹40 per square metre?

The four walls come to $2(l+b)h=2(8+6)\times 4=112$ sq m. The openings remove the door, $2\times 1.5=3$ sq m, and two windows, $2\times (1.5\times 1)=3$ sq m, so the painted area = 112 - 6 = 106 sq m and the cost = $106\times 40$ = ₹4240. The trap ₹4480 deducts nothing; ₹4360 deducts the door but forgets the windows; ₹6160 also paints the $8\times 6=48$ sq m ceiling, which the question excludes.