Figure T shows a closed rectangular tank of dimensions 42 cm by 42 cm by 85 cm with a cube of edge 21 cm glued to its bottom right corner. The tank contains 90 litres of water. Figure U 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 U 
= 42 - 21
= 21 cm

Volume of water under the cube in Figure U 
= 85 x 42 x 21
= 74970 cm³ 

1 ℓ = 1000 
90 ℓ = 90000cm³ 

Volume of water beside the cube
= 90000 - 74970
= 15030 cm³ 

Base area of water beside the cube
= (42 x 85) - (21 x 21)
= 3570 - 441
= 3129 cm² 

Height of water level beside the cube
= 15030 ÷ 3129
≈ 4.80 cm

Height of the water level
= 4.80 + 21
≈ 25.8 cm

Answer(s): 25.8 cm