Figure A shows a closed rectangular tank of dimensions 42 cm by 42 cm by 75 cm with a cube of edge 18 cm glued to its bottom right corner. The tank contains 90 litres of water. Figure B shows the same rectangular tank lying on its side. Find the height of the water level, in centimetres, corrected to 2 decimal places.
Height of water under the cube in Figure B 
= 42 - 18
= 24 cm

Volume of water under the cube in Figure B 
= 75 x 42 x 24
= 75600 cm³ 

1 ℓ = 1000 
90 ℓ = 90000cm³ 

Volume of water beside the cube
= 90000 - 75600
= 14400 cm³ 

Base area of water beside the cube
= (42 x 75) - (18 x 18)
= 3150 - 324
= 2826 cm² 

Height of water level beside the cube
= 14400 ÷ 2826
≈ 5.10 cm

Height of the water level
= 5.10 + 18
≈ 23.1 cm

Answer(s): 23.1 cm