Volume of cuboid = lbh cu units

Hence volume of cistern = 150 × 120 × 110 cu cm

= 1980000 cu cm

Volume to be filled in the cistern = 1980000 − 129600

= 1850400 cu cm

Let the number of porous bricks placed in the cistern be ‘n’

Volume of each brick = 22.5 × 7.5 × 6.5 cu cm

Hence volume of ‘n’ bricks = n × 22.5 × 7.5 × 6.5 = 1096.875n

Given that each brick absorbs (1/17)th of its volume, t

herefore, volume absorbed by these bricks = (n × 22.5 × 7.5 × 6.5)/17

That is 1850400 + (n × 22.5 × 7.5 × 6.5)/17 = n × 22.5 × 7.5 × 6.5