Dimension of garden:
Length = 120 metre
Breadth = 90 metre
Dimension of brick:
Length = .25 metre
Breadth = .125 metre
Thickness= .08 metre
Dimension of wall:
Height = 2 metre
Thickness = .25 metre
[P.S. This not a homework rather a mathematical problem related to Solid Geometry.]
The number of bricks required to make the wall along the full breadth is $$ \frac{90}{0.125} = 720 $$ Similarly for bricks along the length we need $$ \frac {120}{0.125} = 960$$ Now we have 4 overlapping areas so we need to deduct them $$ 4* \frac {0.25}{0.125}=8$$ Therefore in one layer we have $$ (720+960)-9 = 3352 $$ Therefore for the height of the wall which is 2m we will need 25 such layers So, We need $$3352*25 = 83800 $$ Therefore, we need a total of 83800 bricks in all such that the length of the bricks correspond to the thickness of the wall.
P.S. this problem can be solved by another possible arrangement in which the breadth of the brick corresponds to the thickness of the wall by fortune of co-incidence ;-) the answer of both the cases is the same This is because in the 2nd arrangement we cut one half of the brick and place it next to the other, i.e in the net case we just change the orientation of 2 bricks and since the no. of bricks in each row is the same it does'n change the no. of bricks.
Hope it helps :-)