How many cement bricks does it take to cut bricks in a room 3 meters long, 3 meters high and 2.4 meters high?

You didn't give the size of cement brick, which is usually the case. If this wall is 3 meters high and 2.4 meters high, the area is 7.2 square meters. Then calculate the length of the square area multiplied by the height of the cement brick. The former is divided by the latter, and if it is a solid brick with a width of 2 bricks, it is calculated separately. These should be subtracted from the area of doors and windows you reserved.