l = 15m = 1500cm
b= 30cm
h= 4m= 400cm
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.
