Determine the costing plaster work of room of size 15x20 ft. Take height of room =10ft. Consider two windows of size 5x4 ft,assume rate of plaster Rs.20 sq.ft ??

the area of the room is two side walls and two end walls, so

2*15*10 + 2*20*10 = 700 ft^2

The windows occupy 2*5*4=40 ft^2

So the cost is

(700-40)ft^2 * Rs20/ft^2 = Rs 13200