Answer!!!

Now let x bricks can be put in the cistern  = 1096.875x

So volume of water displayed by   x bricks = 64.52 x

Change in the volume of water after dropping the bricks = 129600 - 1096.875x -64.52 x

Water will not overflow if above volume = 1980000

129600 +1096.875x -64.52 x=1980000
Solving we get

1032.355x= 1787400

X = 1731.381162

So 1731 bricks are required