The figure shows a tank made up of 3 sections. Cuboid S with a square base of side 4 cm and height 40 cm. Cube T with a side of 14 cm. Cuboid U that is 65 cm by 17 cm by 42 cm. Water from a tap above flows down at a rate of 3.3 litres per minute while water is drained out from the bottom at a rate of 2 litre per minute. How long did it take to fill up the tank to a height of 67 cm from the base? Give the answer in minutes correct to nearest whole number.
Volume of T
= 14 x 14 x 14
= 2744 cm³ 

Volume of U
= 65 x 17 x 42
= 46410 cm³ 

2 ℓ = 2000 cm³ 
3.3 ℓ = 3300 cm³ 

Net increase in volume per minute
= 3300 - 2000
= 1300 cm³/min

Height of S to be filled with water
= 67 - (42 + 14)
= 11 cm

Volume of water in S
= 4 x 4 x 11
= 176 cm³ 

Volume of water in U, T and part of S
= 46410 + 2744 + 176
= 49330 cm³ 

Time taken to reach height
= 49330 ÷ 1300
≈ 38 min (Correct to nearest whole number)

Answer(s): 38 min