Volume of Wall = 8m * 6m * 22.5cm

                               = (8*100)*(6*100)*22.5 cm3  (Since 1 m = 100cm)

                               = 800*600*22.5 cm3

Volume of eack brick = 25*11.25*6 cm3

Number of bricks required = volume of wall/volume of each brick

                                       = (800*600*22.5)/(25*11.25*6)

                                       = (800*600*225*100)/(25*1125*6*10)   (22.5 =225/10 and 11.25 = 1125/100)

                                       = (800*600*225*10)/(25*1125*6)   (100 and 10 is divided by 10)

                                       = (800*600*9*10)/(1125*6)   (225 and 25 is divided by 25)  

                                       = (800*100*9*10)/(1125)   (600 and 6 is divided by 6)

                                       = (800*4*9*10)/(45)   (100 and 1125 is divided by 6)

                                       = (800*4*10)/(5)   (9 and 45 is divided by 9) 

                                       = 800*4*2  (10 and 5 is divided by 5) 

                                       = 6400

So number of bricks = 6400