So, total volume of the wall= l×b×h = 1500×30×400= 1,80,00,000 cm^3
Now, volume of one brick= 22×12.5×7.5= 2062.5 cm^3
Volume of wall containing only bricks= total volume of the wall - volume of wall containing mortar = 1,80,00,000 - (1,80,00,000 × 1/12) = 1,65,00,000 cm^3
So, no. of bricks = volume of wall containing bricks ÷ volume of one brick = 1,65,00,000 ÷ 2062.5 = 8000 bricks.