Let me give you a math problem for grade five: Uncle Wang wants to draw the wall and ceiling of a classroom, which is 7.5m long, 7m wide, 3.6m high, and the area of doors and windows is 5.5m2 Find the wall area.

Total area: 7.5 * * 3.6 * 2 = 54 7 * 3.6 * 2 = 50.4 54+50.4 =108.4 (square meter).

The total area minus doors and windows is the painting area: 108.4-5.5= 102.9 (square meter).

The laboratory is 12m long, 8m wide and 4m high. Paint the ceiling and four walls of the laboratory. The area of doors, windows and blackboards is 28.4 square meters, with an average of 0.2 kg of lime per square meter. How many kilograms of lime does a * * * need?

You must calculate the total area.

Length x width = ceiling

Height x width x2+ height x length x2= four walls.

12 * 8+4 * 8 * 2+4 *12 * 2 = 256 (square centimeter)

256-28.4=227.6 (square centimeter)

227.6*0.2=45.52 (kg)