The figure shows a tank made up of 3 sections. Cuboid S with a square base of side 4 cm and height 31 cm. Cube T with a side of 15 cm. Cuboid U that is 63 cm by 15 cm by 41 cm. Water from a tap above flows down at a rate of 3.7 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 65 cm from the base? Give the answer in minutes correct to nearest whole number.
Volume of T
= 15 x 15 x 15
= 3375 cm³ 

Volume of U
= 63 x 15 x 41
= 38745 cm³ 

2 ℓ = 2000 cm³ 
3.7 ℓ = 3700 cm³ 

Net increase in volume per minute
= 3700 - 2000
= 1700 cm³/min

Height of S to be filled with water
= 65 - (41 + 15)
= 9 cm

Volume of water in S
= 4 x 4 x 9
= 144 cm³ 

Volume of water in U, T and part of S
= 38745 + 3375 + 144
= 42264 cm³ 

Time taken to reach height
= 42264 ÷ 1700
≈ 25 min (Correct to nearest whole number)

Answer(s): 25 min